By the time they finally put out Halo 3, it was very old. The campaign was worth some co-op time, but the multiplayer was more of the same and I was tired of it before the beta ended.
Halo 2 multiplayer was more enjoyable, but mostly just because the maps were better, and yet I wouldn't touch any of the games now unless it were for co-op play. I'd say that means it's old to me.