I didn't read Revelations yet, but I think that The Secret Crusade explained and did a lot more with Alta´r than Revelations the game (if that makes sense). The story in Revelations was boring in my opinion. I think it was better in terms of gameplay and I liked the city a lot more, but the story was a pain for me unfortunately. Alta´r's memories could have been better, longer and there should have been more of them (that's why I prefer the book. For example, it explains the relationship between Abbas and Alta´r, a lot better than the game did).
Oh, and the Desmond 'puzzle bits' were dumb. I liked Desmond's backstory, but I think they should have told it in a different way.
Well, I can't wait for AC3. Hopefully it won't be disappointing like Revelations was for me.