I just played through 1,2, and 3; and Halo 1's levels and feel just seem so much larger in scale. I don't know if it is just the idea that it was so ground-breaking, but 2 and 3 while great in their own right, they pale in comparison.

Can't say about Halo 3 since I haven't played it, but I enyoyed Halo 1 more than Halo 2.

Maybe, but in 1 there is a lot of doubling back through levels too.

I like the Halo 1 single player better than the sequels. But multiplayer is Halo 3,2,1.

I liked the original over Halo 3, although I am yet to play Halo 2.

No, its not just you, the single player in Halo:CE was far better than 2 & 3.

At the end of the campaign for Halo 3 I said to myself, "That's it?"

The Health system in the first one was WAAAAY better then the stupid one they put in for 2 & 3, to dumb down the game... It took more strategy before...

I liked Halo 2 story cause you fought in the city,which made it feel like a real war. 

ODST should please the urge to fight in a city.

They definitely got the best story in the first one. But that's what happens for most sequels these days. Hopefully Halo: Reach will be a fresh and incredible story the likes of Halo: CE.