Fears are warranted, but of course some are excited. Black Flag ran really well on consoles and was a good game - and Unity, when you can play it and not run into bugs, is a pretty solid "game", unfortunately bugs and crap rarely allow you to enjoy the game for what it is.
This is the core issue with annualizing a franchise that takes years to make each game. You have different studios and frankly, the quality level of these studios varies a lot. Call of Duty runs into this issue too time to time, where Ghosts was just not that great last year, but Advanced Warfare is great this year. Different studios, different results.
So yes, Unity is a hot steaming pile of poo, but the studio behind it won't have a new AC game come out for 2 or 3 years - meaning the next two AC titles are free from the people who made the last one, lining up the studios behind Black Flag and AC III for the next two entries.