Yeah, if you are just playing offline anyway, then you might as well beat 2 and then go on to 3.
I've played 1 till I'm tired of it and now have 3. My question is, would it be good to play Halo 2 before getting into 3? Offline, BTW.
Thanks.
Depends... Do you care about the plot?
If you do care about the plot, then Halo 2 is essential, because a lot of things happen in Halo 3 that won't make sense (from a story-line perspective).
If you don't care about the plot, and you just want to beat up evil zombies and kill nasty mohawked space bastards, then it doesn't really matter. But three is better overall.