Got Halo 3!
I would recommend it for sure! :) Just beat it yesterday the first time as well! Then I had to go looking for all the Goodies... Having trouble with the skulls though, some just don't seem to be there!?!?! WTF... beats me, haven't found that solution yet but found some good resources for the cool stuff!
I'd give it a 9.8/10 - Very Little Slack for improvement. I'd give them a 10, but the ending was pretty boring for a ending to a Trilogy yet a full game. The last "boss" lame... but that dosen't really stack up when you put down all the modes, map building, co-op campaign (less really cool bosses to fight with your friends), and a smooth transition of it all. Halo 2 seemed really rough and annoying to me. Expecially big areas where you would just get lost on where to go, or long stretches where nothing happened for ever. Halo 3 cut that crap out. Great 360 game, kinda makes me sad there won't be Halo 4. (Eh... Forget Halo Wars)
http://www.halo3planet.com/ - Good Resource of all it.
http://features.teamxbox.com/xbox/2062/Halo-3-Collecting-Skulls/p1/ - Has Pics so you can find those Skulls.