FYI "win" is three letters
Halo CE was a fantastic game, marred only by some repetitive level design here and there. Halo 2 whilst fun never really hit the same spot and I never got into the multiplayer, Halo 3 however was kinda ok singleplayer and I really got into the multiplayer.
The problem for me was that Halo CE was so good when it came out graphics wise, weapon variety, open levels with great vehicles and most of all an epic story line full of twists and fantastic music. I played Halo CE multiplayer fanatically over XBC and me and saint had some epic times.
Halo 2 improved the graphics quite a bit, but the story for the most part was lacklustre and did not have the same punch as "omg flood and omg superweapons" it also didn't have the best levels to play in, not as much open level vehicle fun, more of the "follow this road" type events. Multiplayer was obviously fantastic but for me focussed too much on hectic death match type gameplay, I loved being tactical on Halo CE's large multiplayer maps but Halo 2 didn't seem to offer as much of that.
Halo 3, well graphically the game looks nice but they were a little dissapointing, don't get me wrong, I love the graphics, but technically they're not as astounding as Halo CE's was at the time. There are all these little fantastic graphical touches that you never notice though, like the water effects, pretty brilliant and the fact that the ammo counter on the weapon actually reflects the bullets left in the clip even when you're looking at someone else's weapon, or it's on the floor, completely useless but a great insight into the depth of the engine. As I got crackdown I was on the Halo 3 beta and it hit the sweetspot for me, saint was coming round every night till the wee hours playing the 3 (imo) best maps. Back to more open world vehicle massacres etc... Singleplayer story was ok, but again lacked any punch.
And that is my Halo life lol I don't know why I just wrote all that.