Most shooter fans are a fickle bunch. It's never enough to have a solid multiplayer experience, there has to be some catch, something to set it apart from the crowd. Call of Duty 4 may have given us the most drastic change in the old form with it's leveling system complete with new abilities and weapons unlocked as the player gains levels. It was such a success that almost every shooter under the sun has re-worked that system to some degree.
The trouble with this run of shooters is many end up looking the same. What made the system work so well for Call of Duty 4 was the organic feel the leveling system had. Nothing felt over-wrought or wedged in. There were no square pegs in round holes.
So as you've guessed by now, Resistance 2's multiplayer uses a similar system. When you start a match and whenever you go to the menu in a game, you are given the option to change your weapon loadout and pick your "berserk" ability. This ability is charged by accumulating kills and even just hitting an opponent. As you fire at an enemy, you'll see a steadily climbing counter appear on your screen. This translates into a bar that, when full, allows you to use abilities like invisibility, damage buffs and shields.
Luckily, the system has been re-worked enough that it fits with the overall aesthetic and lore of the Resistance universe. The abilities don't take long to charge, and dying doesn't take away your accumulated energy. That's a good thing, because it's not hard to get killed.
Resistance 2's multiplayer experience is fun. It isn't mind blowing by any means, but the Resistance series was never a ground breaking venture. It's a decent shooter all around and offers an experience in line with most people's expectations.