Admittedly I liked Revelations (more than Brotherhood, less than 2 and 1), but 3 just really goes far, far away from what AC1 and AC2 did.
Perhaps it was just the freshness of the environs that compelled me; Constantinople seemed a more interesting and dense place to explore than Rome (but i think Rome just overdid the Italian setting), and the codex entries are still interesting (can't say the same for 3, they were badly handled to say the least).
True, Ezio is over-armed (though the customisable bombs are fun to fool about with), over-powered and the FUCKING KILLSTREAKS are still there, which defang the combat - and any threat beyond desynchronising because you lost the target or whatever - COMPLETELY. True, the assassin-management is largely a series of menus with no strategy beyond taking percentage risks and the tower defence game is utterly pointless (and only necessary if you really, and I mean *really*, slack off doing your assassin-training missions). BUT there's still something to like in there; can't comment on the multiplayer either, but far as I'm aware it's devolved into the typical ghost town populated by either hackers or maximum-rank players steamrolling each other that AAA games tend to devolve into.
I certainly liked it more than Brotherhood and 3; but had I bought it at full-price on release I don't think I'd be being so...charitable.