Bungie somhow managed the impossible, and created a vast improvement on the amazing Halo CE
Halo 2 has a very high quality campaign mode, with some levels which keep you coming back time and again. Each level offers some extremely engaging gameplay, although some levels seem to drag on too long leaving you wanting to reach the next stage. I find in particular the vehicle-based levels can become repetitive after a while. In contrast, many of the levels (particularly the foot-combat Master Chief levels) offer some of the best fun I've ever seen in a campaign mode. Many of the levels played as the MC make you feel actively involved in the story line, and you find yourself willing the human forces to succeed. Punching a Prophet to death while floating on a flying chair never fails to make me laugh. The addition of a Convenant storyline is a refreshing change. Playing as the Arbiter provides a slightly different angle to the game, as it provides you with different allies, different enemies, a different point of view of the storyline and slightly different abilities. Despite this, I often find myself wanting to skip these levels to carry on the human fight. Even though the campaign is neither as long nor as consistent as that of Halo: Combat Evolved, this is not a major problem because of the addition of an XBOX Live component.
The graphics on Halo 2 are sound, and just like all the best games seem apparently age-proof: the graphics still look good even now a year later. Many of the campaign levels offer dazzling cinematic battles and backdrops which add to the aesthetic quality. There are few graphical glitches, and the graphics on a whole are very technically sound. The only negative point to be made about the graphics is that there is very noticable "popping-in" of textures on some of the cut scenes. This is because Halo 2 was one of the first games to have actively animated cut scenes. What this means is that your XBOX is constantly texturing and animating all the objects and characters seen in the cut scenes, instead of the game simply spooling a video file off the disc. However, this is not a major problem and does not means that there are no loading screens between the levels, making the general flow of the game smoother. The sound quality of the game is also very solid, although some of the weapons do sound under-powered.
Apart from all this, the one quality of the game which makes it a true classic is its multiplayer. This is the one feature of the game which will keep you entertained for hour after hour, and it's blatently obvious that Halo 2 was designed as a multiplayer game. It offers everything, from deadly serious games which inspire a colossal will to win, to laughable games which have you in tears, to relaxed games for casual gaming. No matter how you play the multiplayer, it offers some of the most memorable moments you will ever experience in a game. The multiplayer is incredibly well balanced, with advantages of weapons and certain positions being obvious but never impossible to counter, and this inspires a tactical element to the game. The maps are all works of true genius, with the larger ones providing tactical thought exercise for larger groups and the smaller ones providing close-up, frantic fun. The sheer volume of possible game-types means that you'll never get bored of the game: if you're tired of team slayer? Simply switch to free-for-all crazy king on midship for a bit of a break, or CTF classic on Coagulation for a more tactical game.
The Live component is the best of any game yet, offering matchmaking games for organised, sersious gaming and custom games which allow you to play whatever you want with your friends. Matchmaking offers ranked games for driven, well-organised encounters and unranked training matches to hone your skillz. Either way, Halo 2 on Live is sure to be fun, and it is my belief that if you don't have XBOX Live you can only experience 30% of what this game has to offer.
Verdict: in my oppinion, possibly the greatest game the world has ever seen, definitely the greatest FPS. Keeps you coming back for more and more, Bungie's masterpiece. Could barely be any better.