The success of the Xbox 360 has been staked largely on "Halo" and "Gears of War," but the PlayStation 3 has never had a flagship shooter. Into this gap Sony once again tries to shove "Resistance," a much improved but still significantly flawed sequel to the disappointing 2006 original. The massive, deep and accessible online multiplayer modes will appeal to a core group of fans, but the miserable single-player campaign leaves "Resistance 2" as more of a party barge than the flagship Sony needs.