liking this game really depends on how much you've invested into the franchise prior to Halo 3....
So Halo fans main reason to play Halo 3 is just to get through the game to finish the storyline and then to play the multiplayer. However i'm not seeing all the big fuss about the storyline because it seems rather shallow with no real character development and no real plotline at any time through playing. Your just getting a basic FPS standard storyline to give you a reason to move to a new area and shoot more bad guys. It's just not interesting enough to make me care about any of the characters like i got in games like Metal Gear Solid or Max Payne or Final Fantasy etc etc. Also more faults with the storyline come with things like them just dropping plot from the second game and not explaining everything, which was probably done because Halo 2 trashed the story and noone liked the alt character the Arbiter.
Halo 3 also suffers from the same boring game design of the others, not so much but still enough to make me bored. I don't like how the game seems to make you backtrack through the levels some of the time and what makes that worse is how repetitive the levels are. It feels like they've just made alot of corridors and stuff and just pasted them over and over again so it feels like a pattern you'd see on a carpet or wall paper or something. The actual gameplay is esactly the same as Halo 2 and you'll see no improvement from it apart from a few additions to the game...
Four player online coop which on paper sounds great and it is a great addition, however i don't want to run through the same single player campaign again but with 3 more people. I found it makes it far too easy also because the games sooo repetitive you don't really wanna run through it again. Other addition comes fromt he deployables like the shield for the x button, however in the single player it's pretty worthless.
For the multiplayer gets the forge mode which is basically a item editor for the maps. Personally i think it's worthless and doesn't do anything to enchance the game and whats the point of it? PC games have full SDK's where you can create your own mods and maps and i would have been impressed if microsoft left you with that which would have been a first for a console.
The graphics are very bland and generic and that goes for all the artwork and all the armor and weapons felt pretty bland so did the vehicles, basically it's no UT. Infact the only thing i did like the look of was the chopper vehicle. The Aliens all look very childish which i don't like, sorta invented for a saturday morning childrens tv show. The visuals themselves also just seem slightly better from Halo 2 but nothing that'll amaze you like when you saw HL2 or Doom 3 for the first time in 2003.
The sounds are ok and i like some of the music, it's not award winning stuff like Star Wars or MGS etc etc. but nice. The sound effects are all pretty ok and the only things i didn't like were the poor voice acting and how childish the enemy sounds.
Not to say Halo is all bad because it has a slightly above average story for a FPS and it's fun. The game comes with a nice package of a a average single player and multiplayer so it's worth the money. Just the games not as good as everyone says it is and thats because it's mainly just for the fans and not for the new people so much. It's also pretty polished and you is you like the multiplayer you can't fault the value. The AI impressed me the most for the enemy and they all seemed real great but the only problems was the AI of your friendly's which were just stupid and the Arbiter which was pure pure stupid and got annoying.
So yeah Halo 3 wont change your views of the series and if you didn't like it before then you sure wont now, however it's still a good shooter that'll have everyone buying it who own a 360.