Cartoon Source!
There is a working upgrade system, which steam updates periodically giving achievement goals to be able to upgrade certain characters. Currently there has been 2 upgrade characters release, with more to come.
If you got this game with the orange box, good for you, after you defeated HL2, and played thru Episode 1 and 2, finish portal, then your ready to get lost in this fast action multiplayer. It a good bargain. The game is fun and entertaining, and don't worry about dieing.. you will do allot of that, but you will also take allot of enemies with you.
There is strategy to employ in this game, and it does take team work to gain objectives or defend goals. Over the game play is fun, making it well worth your hard earned cash.