Its not that I dont think black flag is good, but the actual Assassin parts blew. Most of the missions were those tail gate ones and it was obvious you had a pre set path (an issue I never had in the other games). Also since I read up on Haytems story in AC 3..... I knew exactly how AC4 was supposed to end.
I found 3 to be pretty dry, but good. Just good, nothing special
Revelations is the worst in my opinion. The villains were boring, I mean we just had the Borgia, and then.... some guy and this awesome dude Shakulu who we never learn much about. Sure Ezio was good in it, but everyone else kinda sucked, except for maybe yusuf
I give AC1 the pass since it was the first game and was much more limited in what it could do. Its not comparable. AC2 clearly had a budget compared to AC1
I have yet to play unity or rogue.
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Also to add
Brotherhood had the best side missions. They were entertaining, had good stories, unlocked nice things, and I enjoyed doing them. Biggest improvement over 2 since 2 had shitty side stuff, and I like side quests and missions in games, which is just a personal taste. 3 was ok with them, but eeeehhhhhhh not as interesting. 4 was alright