Yahoo Sports is previewing all 32 teams as we get ready for the NFL season, complete with our initial 2019 power rankings.

The Buffalo Bills had a very good offseason.

Their free-agent signings were praised. Most experts said the Bills had one of the best drafts of any NFL team. Buffalo added a lot of talent.

That’s obviously great. And necessary. The Bills didn’t have a great roster last season, though they still won six games. Their depth chart has improved.

And yet, it’s all a mystery until we can figure out what the Bills have in quarterback Josh Allen.

Allen was the most polarizing prospect in the 2018 NFL draft, and there’s still not much consensus on how his rookie season went. He was much, much better as a runner than anyone expected, though that’s not why the Bills drafted him. He can throw the ball a mile, but even his biggest detractors never argued that.

The results were mixed.

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Allen flashed. He clearly has big-play ability. In the season finale against the Dolphins he had three passing touchdowns and two rushing touchdowns, though he also threw a pick-six. The Bills were impressed with his improved decision making late in the season. It’s worth noting Allen was stuck with a very thin receiving corps, a suddenly ineffective LeSean McCoy and an offensive line that had to rebuild on the fly. Also, he was a rookie. Given the circumstances, he was fine.

And yet, the criticism that he was inaccurate carried over. Allen’s page on PlayerProfiler.com tells the story: He ranked 35th among NFL quarterbacks in PlayerProfiler’s accuracy rating, 22nd in play-action completion percentage, 47th in red-zone completion percentage, 33rd in deep ball completion percentage and 34th in completion percentage when pressured. Via the Buffalo News, Pro Football Focus said Allen was last among qualified NFL quarterbacks with a 62.1 adjusted completion percentage (which accounts for things like drops, throwaways and when a QB is hit as he throws), and it was a ghastly 45.2 percent under pressure. Bryan Knowles of Football Outsiders pointed out that Allen was horrendous throwing to his right, the worst quarterback in the league in that measure. Allen’s 52.8 completion percentage was dead last among quarterbacks with 100 attempts. He threw 12 interceptions and only 10 touchdowns and posted an ugly 67.9 passer rating.

Basically, if you liked Allen before last year’s draft, there were enough positives to feel good about. If you thought Allen would flop, you could point to plenty of evidence and feel you’ll be right.

Either way, there’s work to do. The Bills should be happy with the progress they saw as a team last year, thrilled to land defensive tackle Ed Oliver with the ninth pick of the draft and pleased with their free agent haul, and it really doesn’t matter if their quarterback completes 52 percent of his passes again. Allen said improving accuracy was his biggest priority this offseason. He worked again with quarterback guru Jordan Palmer.

“Ball placement is huge, especially in this league,” Allen said, according to the Buffalo News. “The type of concepts that we have, trying to get the ball to our playmakers where they can make some plays, that was a huge emphasis. We’re still working it. That is something that will never change. You always want to try to work on ball placement.”

Allen is never going to be Drew Brees when it comes to putting throws on the money, but he needs that piece to improve if he’s going to succeed in the NFL. That doesn’t make him unusual among second-year quarterbacks. But it was his biggest issue in college, which makes it a critical part of his NFL development.

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If Allen comes along, the Bills appear to be moving in the right direction. While it’s troubling that at some point in each of the last two seasons coach Sean McDermott thought Nathan Peterman was his best option to start games, he has gotten a lot out of his limited roster both years. Buffalo’s defense was very good last season and could be better. The offense will take some time, but there have been many improvements and it could come along faster than expected.

Allen is the lynchpin. If he’s great, the Bills could ascend quickly. If he can’t fix some of the issues that draft experts worried about last year, Buffalo probably isn’t going anywhere for a while. And after Allen’s rookie season, it’s tough to say yet if he’s on the right path.

View photos Josh Allen faces a big second season with the Buffalo Bills. (Getty Images) More

It’s hard to be one of the winners in free agency and the draft, but the Bills did it. Their free agency haul was smart. Receivers John Brown and Cole Beasley and tight end Tyler Kroft were added to the skill positions and the Bills signed six offensive linemen, highlighted by center Mitch Morse and offensive tackle Ty Nsehke. Buffalo realized that a critical piece to Josh Allen’s development was getting him help. Signing All-Pro returner Andre Roberts from the Jets helps too. The Bills made a pick in the draft that could be a great one, stealing Houston defensive tackle Ed Oliver with the ninth pick. Buffalo picked offensive tackle Cody Ford in the second round, and he has first-round talent. Other picks like running back Devin Singletary and tight end Dawson Knox are very interesting. If you’re giving out grades for free agency, and for the draft, the Bills probably would rank in the top five in both.

GRADE: A

Buffalo’s defense is good. It led the NFL in yards allowed per pass play and was third in passer rating allowed. The Bills defense ranked second in Football Outsiders’ DVOA per-play metric. Cornerback Tre’Davious White is a rising star. Linebacker Tremaine Edmunds is young and has tremendous potential. Defensive tackle Ed Oliver has exciting potential. The Bills have done a great job building the defense with young, talented players and reliable veterans. This can be a top-five defense, perhaps for many years.

The Bills improved their skill position group, but that doesn’t mean it’s good. Zay Jones made strides last season but he still has a long way to go to be a No. 1 receiver. John Brown is a good deep threat, but has still had an up-and-down career due to injuries. Cole Beasley is a good slot receiver but not a difference maker. Tight end Tyler Kroft is talented but has 661 career yards in four seasons. And LeSean McCoy’s production fell off a cliff last season at age 30. You’d like to project someone in the offense to be a true dominant top target for Josh Allen, but those players aren’t easy to find.

Josh Allen emerging as one of the best runners in the NFL was one of the biggest surprises of the season. And note we didn’t say Allen was one of the best running quarterbacks. He was one of the best runners, period. After Allen returned from an elbow injury in Week 12, he rushed for 476 yards and five touchdowns in six games. That’s a 16-game pace of 1,269 yards and 13 touchdowns. He did it with an 8.8-yard average. Allen started only 11 games but was the 31st leading rusher among all NFL players.

There was nothing to indicate Allen would have that kind of an impact as a runner. Allen had just 767 rushing yards in three college seasons, though sack numbers count against rushing stats in college. He’s a good athlete, and his 4.75-second 40-yard dash is good for a quarterback, but nothing indicated Allen would be such an effective runner as a rookie in the NFL. Because it was such a surprise and was based almost entirely on scrambles and not designed runs it’s tough to say if Allen will again be so good on the ground, but he clearly has more ability in that area than expected. Even if Allen didn’t expect to put up the rushing numbers he did.

“Not at all,” Allen said, according to the Buffalo News. “Things just kind of unfolded in front of me. We didn't really run a lot of quarterback-run plays. It was more scramble, get outside the pocket and try to make a play.”

Bills coach Sean McDermott said he didn’t think the concept of a “No. 1 receiver” in the NFL existed anymore, or at least was less important. Still, his description of what the Bills need sounds very much like a No. 1 receiver.

“At the end of the day I’m looking for a guy that can affect a defense, from a matchup standpoint, and a guy that people have to be mindful of,” McDermott said, according to New York Upstate.

Additions John Brown and Cole Beasley are good at their roles, but if there’s a No. 1 receiver (or whatever McDermott wants to call it) on the roster, it’s Zay Jones. Jones, the 37th pick of the 2017 draft, had a quiet rookie season and then a bad 2018 offseason that included a weird, bloody confrontation with his brother. He did make strides on the field last season, with a 56-652-7 line. He finished strong, with five touchdowns in Buffalo’s final five games. Jones said this season could be even better.

“[I’m going to] use my hands more, being more physical at the point of attack, being able to high-point catches, and being more physical and dominant in the run game,” Jones said, according to New York Upstate. “So now that I’ve had the time to heal up and add more strength and and add more size, I’m looking forward to going out and being able to compete at an even higher level.”

From Yahoo’s Scott Pianowski: “The Bills added a host of offensive pieces in the offseason, but it's two holdover receivers, Robert Foster and Zay Jones, who make for the most interesting late-round fliers (excluding Josh Allen for the moment). Foster could go outside the Top 10 rounds in most leagues, and Jones might even be undrafted.

“Jones looked like a lost player in his rookie year, but somehow he caught six of the team's 13 touchdown passes last season. There's no deep element to his game, but he's likely to be the team's best red-zone receiver again. There's a pedigree to bet on; he was a second-round pick in 2017.

“Foster was undrafted out of Alabama, a program that seldom has an explosive passing game, but he found a way to get 20 yards per catch as a rookie. After graduating the practice squad, Foster was dynamic in the second half of the season (526 yards in seven games).

“It's hard to say what Allen is ready to do at quarterback, but this team won't throw much to its backs or tight ends, and I have no problem betting against John Brown again. Meet the new boss, same as the old boss. Make sure Foster and Jones are on your sleeper page.”

[Yahoo fantasy preview: Buffalo Bills]

LeSean McCoy averaged 3.2 yards per carry last season. Among all NFL running backs with more than 100 attempts, only LeGarrette Blount averaged fewer yards per carry. It was a startling drop considering McCoy had never averaged fewer than 4 yards per carry over a full season. Was it due to McCoy slowing down at age 30, or the offensive line? It might not matter. There has been plenty of speculation that McCoy will be cut or traded before the season, which would leave veteran Frank Gore and rookie Devin Singletary to handle the running back duties. If McCoy remains with the Bills, he comes into the season in a unique situation for him, having to prove himself once again.

IS THE OFFENSIVE LINE FIXED?

The Bills had a lot of turnover on the offensive line last season, and might have even more this season. It’s possible the team has five new starters on the line, depending on how the team feels about 2018 left tackle Dion Dawkins. They added six free agents and drafted offensive tackle Cody Ford in the second round.

“We made a concerted effort in free agency to add pieces, a lot at the O-line,” Bills general manager Brandon Beane said, according to the Democrat & Chronicle. “We were not happy with our O-line play. It was inconsistent. There was an effort to fix a lot of that in free agency. We also wanted to add youth. Sean said it, we believe in winning up front. There were frustrating times with some of the games we didn’t win last year, I think it came down to losing the battle up front. I said if nothing else, this year we’re going to fix that.”

Tackles Ty Nsekhe and LaAdrian Waddle, guards Quinton Spain, Spencer Long and Jon Feliciano and center Mitch Morse were signed. Along with Ford, there are a lot more options for the Bills up front. The challenge will be finding the right combination before Week 1.

It’s easy to see the Bills establishing themselves as the No. 2 team in the AFC East, being in position to pounce if the Patriots and Tom Brady ever slow down. Buffalo is building a very good defense. They’ve added a lot to the offense. If Josh Allen harnesses his talent and smooths out the rough edges of his game, the Bills could take a big jump and perhaps even be playoff contenders. Sean McDermott has shown he can maximize his talent on hand. And if Allen proves to be a franchise quarterback, the Bills’ future will look very bright.

The Bills can be very good around Josh Allen and still be in trouble if Allen’s inaccuracy keeps him from being a standout quarterback. The offensive cast around Allen is better but still might not be great, and how that group plays is key for Allen’s all-important development. Allen can be the reason the Bills ascend, or his inconsistency could be what holds them back for the next few years. The Bills could practically have a repeat of last season, including Allen’s up-and-down play, and that wouldn’t be ideal.

In a perfect world, the Bills’ offensive improvements fit and Josh Allen takes off in his second season. But until that happens, there should be some skepticism. The Bills defense is good enough to keep them in most games, but this season anyway, the offense won’t be good enough to get them to .500.

32. Arizona Cardinals

31. Miami Dolphins

30. Oakland Raiders

29. New York Giants

28. Cincinnati Bengals

27. Tampa Bay Buccaneers

26. Washington Redskins

25. Detroit Lions

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Frank Schwab is a writer for Yahoo Sports. Have a tip? Email him at shutdown.corner@yahoo.com or follow him on Twitter! Follow @YahooSchwab