Has its good and bad sides.
On one hand, the gameplay is pretty arcady and played in co-op can be pretty fun.
On the other, the levels are considerably bigger than the first game and in the standard Serious Sam style, you have a lot of enemies coming straight at you and those two things combined can make things pretty crazy, fun and frustrating at the same time.
Story is mostly just there (though is amusing) and the graphics have their charm.