I think you have to remember, that all endings are connected to the beginning of the next game. Sure, *** SPOILER *** Lucy "dies" and OHMYGOSH oh no, but that doesn't make it a bad ending - merely a shocking one ***SPOILER ENDING ***
Anyway remember that the ending is probably joined to the beginning of AC: Revelations - besides, I still think Lucy was a Templar. Did any of you see the tracking device on her desk? Mmmh?
All in all; I do not think it's bad ending, actually I think it was rather good - it made me want to play AC:Rev instantly and it also made me wonder who the hell that Michael-guy is and what the deal is with all this secrecy!