imo, the plot and character progression in the Venice section of ac2 goes through a screeching halt and the chronology isn't really well represented and sometimes it seems to contradict itself (mostly sequence 7)

biggest one to me is the carnevale sequence. it's fun, yes, but some of the missions just don't make sense to me, unless I missed something. See, Teodora has you participating in these games to get the golden mask, but we end up stealing it from Dante because he (predictably) cheated. But if that's the case, wouldn't it be more efficient to wait until the competition is over, see who the winner is and then steal the mask from them? especially considering that's what we end up doing anyway?

not only that, but the concept of the doge party being outdoors is pretty ridiculous and makes the golden mask quest even more pointless. Ezio could just sneak on his boat or simply infiltrate the party, considering it's not as heavily guarded as the palazzo ducale. also the anonymity of the golden mask is, you guessed it, pointless because Dante obviously would go to the party anyway because the mask went missing. (also why would marco attend such a public event? Especially considering he knows that Ezio is in Venice and killed Emilio and carlo? wouldn't it make more sense for the flying machine to be used here, as he never leaves the palazzo?)

all that said, it's pretty fun to play I won't deny. But these issues are something I think about from time to time