Agree on Red Dead Redemption. Was very good overall, even though the online was a bit crap.
As for Assassin's Creed, what I played was ok but when I played them back to back, I basically got burnt out and wasn't really enjoying them in the end.
My general opinion:
1st - Can see what they were doing but very repetitive. Altair was boring as well.
2nd - Personal favourite of those I played. More side missions with more variation and Ezio was a good lead. Liked the story as well, though thought the final boss was ass.
Brotherhood - Also very good. Really liked ways to build your own Creed, sending them out on missions etc. Plus playing about in Rome was always fun.
Revelations - Meh. Couldn't get into this one. Hated the tower defence game (though ironically made you play the game more as an actual assassin ) and wasn't arsed with the bomb crafting. Also by this point that it started to feel too samey.
3 - Ambitious but didn't really like it, namely because Connor just came across as a whiney asshole, which put me off.
That's where I finished as I didn't play much of Black Flag and Unity was a buggy mess when released. By the time Syndicate came out, I was already a bit behind and had no real interest in getting up to speed.