I'm at the same point. Just completed sequence 8 and am not liking the storyline missions one bit. The last ones I did were especially crappy if you ask me (locating/chasing the one guy, the prison, and the execution).
I've spent tons more time on the random tasks - hunting, taking over forts, trading, collection, and homestead/liberation missions - and just plain exploring than on advancing the story. This weekend I want to just plow through the story so I can get it over with. Then I can go back to having more fun.
i havent finished the game yet just started with the fully grown character, but so far the only fun part was sailing the pirate ship and blasting other boats. the main mission was boring as hell, playing his dad was awful. playing as a child that hunches like a hunchback was uncomfortable. you cant kill random people unlike AC1 which sucks, redcoats suspect you too easly the whole blending in the crowd is gone.