It may be for the best to drop it. Frankly, the modern stuff was one of the weak links of the series for me.

ACIV is in my backlog, I simply burned myself out on the franchise back when ACIII came out and simply got distracted by other franchises, so I have yet to play it but have heard good things. I actually liked ACIII as well. I just didn't really see a point in continuing the series after Desmond since he was central to the plot in the beginning and his story conclusion was rather dull.