Well the campaign is great, but then I'm going back to Gears.
I dislike Reach tremendously. Even after a title update the game is clunky and doesn't play like any old Halo. I adapted to H3 and I began to like it. I gave Reach a few months and never cared for it. I used to get pissed when I lost a Halo 3 match. I don't even care if I loose/quit in Reach. The additional CEA maps were great for MP, however they don't play at all like they used to.
In my opinion, they made Reach to compete with other game titles, and ignored the fanbase. The fans that made this series were left in the dark. So now you have the big load of players that left for other games, and yep only about 60k people online. Halo 3 still has 1/4 of that. Dedicated halo players will always play. Once 343 realizes that, they'll make a game thats worth playing.
Ideally,
Mixture of H2/H3 for me. Never got to stress test H1 MP gameplay, for the sole reason that it wasn't there.