i have tried brotherhood and decided it should have been DLC or included in previous game, i doubt i'd pay much for it. Revelations has been eh with all of my friends so i stayed away as i'm not a big AC fan. i think the second one just really turned me off of it. constant hand holding, impossible to die basically, i did not like ezio at all... all personal dislikes of course.
if i like ACIII i might go back and try Revalations. there were a few things in the gameplay trailers that i could already tell would be boring and repetitive, but the new features/setting has me interested.