Free to play online shooter, done in a tongue-in-cheek cartoon style.

User Rating: 9 | Battlefield Heroes PC
You can't go wrong with this game, if for no other reason than it is free. The game does support micro-payments, so that you can permanently buy higher-end weapons, or play dress up with your character, but if you are good at shooters, you can do fine just fine with basic "free" weapons. In fact, many look down on those who pay for their weapons. There are also points you earn for completing missions, or even just for logging into the game, that you can then spend to acquire the higher end weapons for a shorter amount of time (1 or 3 days). The shooting is dead on, with the three classes balanced fairly evenly with a tank type, and medic type and a sniper type. There is also an RPG type element in that you gain access to skills as you level up. You can reset your skill points at any time for no penalty, so you could decide, for instance, to reset your sniper and put all his points into poisoning his knife blade.
The biggest downside is that, like most online shooters, you have the occasional hacker who has no skill and for whatever reason, wants to ruin the game for everyone else by cheating, instead of doing something productive, like neutering themselves for the good of society. There are also occasional lag hitches, but I remind you that the game is free. I personally think this is the most entertaining free multiplayer online game out there right now.