This is the type of post where I will most certainly be flamed but just wanted to point out some things.
After having rented Halo 3 (Yes rented because I truly despise the Halo franchise and was only ever impressed with Halo 1 but still hated it due to my friends.) I have this to say about the 640p. If you can tell the difference between it and the 720p then you have much more awesome eyes than I do. Personally Halo 3 to me looks EXACTLY like Halo 1 just with better polished graphics. Now while this is outstanding for fanboys that just drool when anything halo comes their way for those of us casual gamers we really expected MORE especially with all the hype. To say that the graphics are bad at 640p would be a complete rip on Halo and Perfect dark which visually are pretty games. However, I think what annoys most people is when I think of showing off what the 360 can do as far as visually I usually show my friends Bioshock. True the levels are ridiculously small and you can beat the game in less than a few hours but it's a BEAUTIFUL game. Halo has large levels but the gameplay is still halo, still rehash of of 2 which was rehash of 1. Same story line and can be beaten even faster than Bioshock. Just a game. The 640p actually is fitting since Halo was supposed to be the second coming of christ and afterwards most people (not fanboys) are just accepting that it's the second coming of another generic game.
So at the end of the day what have we learned?
Halo is fun if you are into that type of game. Visually it's about as impressive as a monkey shaving it's ass.
Are there games that show off what the 360 is really capable of? Yes! Go rent Bioshock. Flawless game except that their is no multiplayer which after you beat the game means time to take it back to gamestop. (so rent it first!!!!)
*steps down* Ahem... Thank you for your time.

I think people don't understand that graphics are not the only thing that pushes a system's capabilities. There are a lot of things going on in Halo that you don't see. Every game you play in matchmaking, every campaign mission you play is reviewable in the theater where you can detach the camera and explore anywhere in the map. Halo may have sacrificed some of the graphics for more entertaining maps and features, which IMO makes a better game. I thought GOW was outstanding when it came to graphics. However, I felt myself getting bored very quickly with the closed in maps and features. Not very replayable.
I appreciate the fact that Halo is not your type of game, but there's no need to bash it when it has revolutionized online console multiplayer with Halo 2 and now with the advent of theater based review and forge editing options. The Bungie developers push the boundary for other games. Plus the ganmes are fun as hell. I strongly suggest you re-rent it or buy it, as it will give you hours of enjoyment beyond just "beating the game".
On another note, why did you hate Halo1 because of your friends? Did they beat your ass all the time or something? If that's the case then I can see why you don't like Halo 2 or Halo 3. I'm not being sarcastic. I've got friends that don't play multiplayer because they're not good enough. I wouldn't want to go be someone's bitch either, so maybe you should stay away from multiplayer.