I did not play Halo 2 or it's predecessor, Halo...but I am impressed w/ Halo 3. Just wish the story didn't have to end.
My reference games are: Gears of War, GRAW, GRAW2 and Rainbow 6: Vegas. I never really liked FPS/Tactical shooter-type games before these 4. The last FPS style games that I enjoyed and was competitive as a gamer were Quake, Quake II and Quake III. So, my experience with Halo 3, is that of a newbie.
I happened to rent a copy from Gamefly (since my pre-ordered Limited Edition version didn't arrive until a week and a half after the game shipped & happened to have scratches all over the 2 discs - even though they are still playable). Day 1 (Monday - 10/01): Played Casual, found the game to be way too easy but it allowed me to explore the world a bit. Got 1/2 way through the game in what seemed like a few hours. Had a bad headache from playing.
Day 2 (Wednesday - 10/03): Played Multi-player, found that playing against 3 other players wasn't as much fun compared to playing Rainbow 6: Vegas. Only lasted a few rounds before I was bored and turned off the game and went back to playing Rainbow 6. 30 min tops.
Day 3 (Saturday Night - 10/06): Visited my friend (who originally got me to buy the game in the first place) and played Halo on Normal mode via Split screen on a 32" TV (gave me a headache, but after tweaking the controls here & there, I was fine). Played from 9pm to about 11pm, maybe 12 am. Day 4 (Monday): Played Campaign mode on Heroic mode, as a continuation of my last gaming session with my friend. Played from about 9pm to midnight. 3 hours
Day 5 (Wednesday): Continued campaign mode w/ friend from 9pm to midnight. 3 hours
Day 6 (Thursday): Became more and more immersed in the game, played from 8pm to 1am. 5 hours
Day 7 (Friday 10/12/2007): Marathon gaming session, played from approximately 8pm on Friday until about 7am on Saturday morning. A few frustrating levels and finally...the end of the game! 11 or so hours Overall, I only found 2 skulls. Only found 3 (2 usable) golden eye information terminals but, I am impressed and satisfied with Halo 3. The music, the visuals, the gameplay, the art, environment, the story! Spectacular.
It's like an RPG w/o having to worry about levels and states. I found myself looking forward to where the story could lead me and what kind of new equipment I could utilize on the upcoming missions. A lot of fun for this type of game, I just wish the campaign was longer. I really, did not want the game to end. Which is why, I'll be playing it again, on the Legendary difficulty.