Not as good as Halo: Combat Evolved
Another major flaw was the A.I. which was unrivaled in the original seems to be lacking in Halo 2. Whereas before the A.I would dodge a lot more in this they seem to just stand still and fire with pinpoint accuracy and you are unable to strafe their attacks which is very annoying.
The single worst flaw is the elites energy sword which was something to be worried about in the original is now laughable as sometimes when an elite swipes you with his sword it doesn't do any damage at all (try standing still next time you see one).
The flood are also lacking in the I.Q department and the levels with them are unparralelled in terms of boredom and frustration. They just seem like a bunch of drunken frat boys running frantically at you in small numbers. (At least there was a ton of them in the original).
The story is a jumbled mess from start to finish and the fact that they try to make you sympathise with the coolest bad guys in any game or movie (elites) is sickening and replace them with idiotic brutes is insulting.
If it wasn't for xbox live it would have been a lot worse