I'm really liking the multiplayer so far, especially after the garbage multiplayer of Reach. Armor abilities are actually implanted in a good way (so far) compared to armor-fucking-lock in Reach (really ruined the gameplay. It really slowed down the game, in a bad way. I don't like the fact that the normal slayer rotation is only 5 maps, however they are all decent to good so it's not a huge problem, and DLC is already coming in december.
I have played Halo 3 for at least a good 700 hours, Halo 2 something around 100 I think, Reach less than 50 because it sucked so hard and Halo 1 only splitscreen, Multiplayer-wise, my favorite Halo's would be:
Halo 3 > (*I think*) Halo 4 > Halo 2 > Halo 1 > Halo Reach