In an esports world filled with first-person shooters and MOBAs, a simple card game, Blizzard's Hearthstone: Heroes of Warcraft, has carved out a sizable audience of its own.

Magic: The Gathering's simpler cousin adds a sizable dose of poker's game-swinging surprises to its animations and voice acting, setting the game apart. Sometimes referred to as "wizard poker" by its fanbase, Blizzard's concoction has proved a rather alluring brew.

Hearthstone's brand of fun, suffice it to say, has sold quite well. Back in November, Blizzard reported there were 40 million active Hearthstone accounts. Back in July, Hearthstone's official Twitch stream featured hundreds of thousands of viewers tuning in not to watch a Hearthstone championship or tournament, but just to see the announcement of a new expansion set.

"One of things that we didn't anticipate was the amount of traction with stream audiences on Twitch," said Jason Chayes, production director for Hearthstone. "Internally, we had a bunch of tournaments that were really fun to watch and that was exciting to see, but it was definitely not something that we expected that once we got to the beta, people would start stream themselves playing Hearthstone and that would develop a wide following."

Due to the interest in Hearthstone, the development team at Blizzard had to increase in size.

"By the time we shipped [Hearthstone] in March and April of 2014, we were 15 people. The main development group that works on the game itself is called Team 5 and that's about 52 people right now. Beyond that there are probably around 20 more people that we're partnering with," said Chayes.

Poker stars Daniel Negreanu and Bertrand "ElkY" Grospellier face off at BlizzCon. Blizzard

With so many people playing the game, Hearthstone has found its sea legs in the wild world of esports. A card game is a very different type of game than League of Legends or Dota 2, serving to broaden the esports landscape rather than directly competing with an existing game. Yes, Magic's more than dipped their toes into the online world, but the bulk of that game's strength on a competitive label remains its live Pro Tour, not through its occasionally clunky online interface.

One main difference between Hearthstone and other card games like poker and Magic is Hearthstone wasn't adapted for the Internet, but was designed for the Internet. There's no paper equivalent of Hearthstone that the online game needs to reflect, giving the game designers considerable flexibility to make changes. Cards in Hearthstone aren't simply static rectangular objects with information on them, but through sounds and visual effects, feel very alive.

Hearthstone games are one-on-one battles, so the team dynamics are out (at least on the individual game level). It's a slower game of discrete actions, similar to other card games or board games such as chess. Big moments interspersed with deliberation makes providing in-depth analysis a simpler task and provides a less bewildering experience for a casual viewer who many not be as familiar with all the game mechanics.

This March, Hearthstone hits the two-year anniversary since its official release from beta, so it's a mature game, not a hot new release. The game's maturity provides Blizzard with new challenges and difficult decisions as the game continues to develop.

One of the most controversial aspects of Hearthstone's development is the increased inclusion of random elements on cards. While there were always cards that had such randomized elements back in early beta, such as Mad Bomber making three randomly targeted one-damage attacks when summoned or Sylvanas Windrunner stealing a random enemy minion at death, the number of random mechanics has increased over time.

"We think randomness is a very important part of the game. Random leads to a lot of novel situations and a lot of fun surprises, but our overall philosophy has been that randomness and skill are not mutually exclusive," said Chayes. "You can have a game that has high randomness and high skill and they can co-exist, such as in poker ... We feel that Hearthstone is another game that has high randomness, but is also a high skill demanding game."

One way Blizzard has dealt with this is a new mechanic in its most recent mini-expansion pack (dubbed "Adventure" by Blizzard), the League of Explorers. Denoted as "Discover" instead of drawing a random card or creating a random minion or spell, a common theme in Hearthstone cards, Discover offers a more controllable type of random number generator (RNG) by allowing the player to have choices among random selections, not simply have the game draw one "out of a hat."

The Discover effect has been better received by the community than some of the more randomized effects from previous expansions, but will this mechanic do enough to increase the skill cap of the game while keeping the "big moment" swings alive?

"RNG is good for casual players because it helps even out the skill level among players," said CompLexity Gaming's Kacem "Noxious" Khilaji. "When you have some form of control over the randomness, it still appeals to the casual crowd, but it also means that the more-skilled players don't have to just roll dice. They don't just have to say 'Well, if RNG happens, I'll have no say in it.'"

Even if more controllable, the randomized effects are here to stay. These surprises that pop up, while frequently providing wild swings in gameplay that a player has limited influence on, also provide Hearthstone with a kind of emergent gameplay, creating unintended and/or unusual situations for a player to have to cope with.

Carlton Beener/ESL

Most Hearthstone tournaments feature best-of-five matches, quite a small sample size for a game with such an element of probability. The World Series of Poker consists of hundreds of thousands of hands before the prizes are given out. Fortune is a large element in baseball, a sport of bad hops and convenient large drives, but baseball teams also play 162 games in a regular season (and even then the luck doesn't all conveniently even out).

Noxious says this is a tricky problem for Blizzard to solve: "Because the way Hearthstone's designed, you can't have as many hands as you do in a game of poker. There's no way to shove enough volume into the game to reward the most-skilled players. So realistically, the only way you can modify that is by toning down the RNG or at least reducing the variance so that the spread isn't as obscene."

Another issue is with three adventures, each introducing a few dozen cards and two full expansions with over 120 cards apiece, how does a new player catch up? Even for players who are willing to pay real money, shelling out for $70 and still missing most of the game's popular cards may be a lot to ask.

Blizzard is not unaware of the issue with casual players and the additional obstacles a large number of cardsets can bring.

"The question is how do we deal with new players coming in and asking themselves what are the optimal cards from Naxxramas or out of the Grand Tournament or out of the League of Explorers," said Chayes. "We think we have a pretty good plan in place and some ideas. We're not quite ready to go into all the details, but we'll have a lot more to share about that pretty soon."

Another issue affecting both casuals and professionals is the proliferation of bots, sophisticated computer programs, that play games for the person, on Hearthstone's ladder. This isn't just a Hearthstone-specific problem, but one that affects many other games. Blizzard has taken an active role attempting to eliminate as many of these bots from the game as possible, going back to last October's ban of thousands of accounts for automated play.

With Blizzard actively pushing esports more now than in past years and Hearthstone's ability to get people to pay for virtual cards with real money, they have incentive to deal with the game's growing pains.

In the meantime, players will keep opening packs and both revel and despair in the surprises that each game brings. And silently cursing at that obnoxious Secret Paladin who always has the right card on Turn 6.