There are five different character classes available: boxer, firefighter, rocker, slugger, and blitzer. Each has a completely unique primary, secondary, and special attack, so you'll need to master them individually as the gameplay changes a lot depending on your character class.
You can also customize your character with different items, weapons, and accessories that not only change the appearance of your character but also provide various bonuses during the game.
The game has several different modes. Normally it's one group against another. With different modes, though, you can change the objective of the level or make it so the levels contain destructible elements that you can try to use your advantage.
The graphics are excellent, and the look of the game is reminiscent of Team Fortress 2. The optimization is also very good, so you shouldn't have any problems even if you're using a mid-range computer.
Brawl Busters is a fun game with hundreds of hours of gameplay. And, best of all, it's free. Just download the client and start busting heads.