Join GameSpot as we celebrate gaming history and give recognition to the most influential games of the 21st century. These aren't the best games, and they aren't necessarily games that you need to rush out and play today, but there's no question that they left an indelible impact on game developers, players, and in some cases, society at large.

It's hard to explain what it was like to be a console first-person shooter fan in 2001. While PC players had been enjoying FPS games for years, the experience was never as strong on consoles. Where PCs had the fluidity of the mouse-and-keyboard setup, controls on console struggled to capture the same feel--to this day, two of the best-regarded FPS games of the era, GoldenEye 64 and its follow-up, Perfect Dark, were played with controllers that didn't even sport dual analog sticks. In the nascent days of console online multiplayer, squaring off against other players, the thing that could really make shooters exciting, was limited to split-screen battles (often on tiny TVs). There were standout titles of the era, of course, but the FPS field was nothing like what we experience today.

Imagine, then, the arrival of Halo: Combat Evolved. For the first time, the discussion around console shooters opens up to a huge number of new possibilities. The Xbox's system link multiplayer, the console market's first experience with LAN, meant you could play with seven other friends--and more than that, you could work together as teams and execute tactics that your opponents couldn't anticipate simply by glancing over at your side of the screen. For those whose gaming consisted purely of console experiences, it was the first time a shooter experience would become something similar to playing paintball or laser tag. It was a glimpse of the possibilities of the shooting genre's future, and it was glorious.

Halo's arrival on the console FPS scene didn't just herald the shooter future, it manifested it. From the jump, the game was unmatched. In the very first mission, as players took on the role of genetically enhanced supersoldier Master Chief, developer Bungie was throwing together elements that shifted how playing shooters felt on a fundamental level. First and foremost was the enemy design. The alien Covenant were generally not idiots--they fought hard and smart, taking cover when they were hurt, grouping up to channel their fire, throwing grenades to flush you out of your hiding places, and charging up when they knew they had you on the ropes. Every encounter with an Elite enemy in the original Halo was a harrowing one, because the bastards weren't just tough and didn't just absorb a lot of shots. They were also very good at finding ways to kill you (and never missed a chance to laugh about it afterward).

Bungie set a standard with enemy AI design in Halo. But it also did a lot to make its fights feel more like battles, capturing a feeling that many shooters have chased ever since. The mostly-pretty-good AI extended to allies as well, and much of the time in Halo, you're fighting the Covenant with the support of a squad of UNSC Marines. You might be a one-player army in Halo, but you always felt like part of a team, and excited shouts of your squadmates as you take down a big enemy or set off a big explosion (as well as their cries as they got blasted by grenades) created the sense that there was more to Halo than just your role in the game. Few titles captured the feeling of stepping straight into a full, realized world the way Halo did, and a huge part of that was the idea that you were just one (really good) soldier in a much larger, active army.

Halo felt like it was doing something video games had always wanted to do, but had never quite achieved before.

So many of those battles managed to take on an epic scale thanks to Halo's perfect combination of elements. Huge fields often had vehicles crossing them, some of which you had to deal with on foot, others which you could battle in tanks or Warthogs of your own, with marines jumping into the gunner positions to back you up. A phenomenal soundtrack and Bungie's cinematic approach made those moments even more exhilarating, expanding the scope even further. The game's smart level design gave you tons of agency--you could pick your way through engagements, slamming straight into enemies or finding ways to flank them out while your squad distracted them, hunting down vehicles or rocket launchers to turn the tide in your favor, or sneaking past enemies and avoiding fights altogether.

Halo felt expansive in a new way for shooters, setting the tone for massive, cinematic, action movie-like games that would follow. Level after level, Halo felt like it was doing something video games had always wanted to do, but had never quite achieved before. It wasn't necessarily inventing new things, but it took the best ideas of the genre and turned them into a singular experience. When it comes to the AAA shooter experience as we now know it, Bungie cracked the code with Halo.

Shooters are still feeling the influence of some of the best and freshest ideas of Halo. The ability to carry only two weapons and think strategically about which you pick up? Halo. Recharging shields that force you to find a shady spot and consider your tactical options mid-fight? Halo. Grenades on a trigger button, ready at all times? Halo. The standard in console FPS control schemes? Halo again. The franchise it spawned was such a powerhouse that for years, developers and publishers hoped their games might become the "Halo-killer" to usurp its place at the top of the shooter heap.

Bungie elevated console shooters with Halo, but the even bigger lasting influence of the game might be how it shook the console landscape by legitimizing Microsoft's Xbox. When Microsoft decided to leap into the console market, there was no shortage of skepticism, but Halo was the reason to purchase the new machine. The game proved that Microsoft was not just some late-comer trying to use an abundance of cash to muscle out the dominant PlayStation, and it would be Halo's sequels that helped make Microsoft a bigger force through Xbox Live. Through its role as an Xbox exclusive, Halo helped lay the foundation for the next two decades of what gaming would become.

Halo changed the conception of what games could be for a lot of players. It rocked the shooter world with ideas that have become standards to this day, and its approaches to gameplay and presentation made for that truly "epic" experience that games have continued to try to capitalize on ever since. But more than anything, it altered gaming for console players, elevating the experience with an amazing single-player campaign, a huge and expansive game world, and the first steps into the future of multiplayer. Playing Halo in 2001, it felt like things had changed--almost 20 years later, we're still feeling the shockwaves.

For a look at the rest of our features in this series, head over to our Most Influential Games Of The 21st Century hub.