I'm not sure that I would say this counts as something that I didn't like, but there is something that I couldn't completely figure out even after having read the book.

It always confused me what Vito was trying to do by having Luca try to give the impression that he wanted to trade families. Given Luca's famous loyalty it would seem to me that nobody would believe that it's possible he would do something like that. Thus, I have to wonder if the Don didn't take this into account and knowingly led his most feared enforcer into a death trap. If so then to what end did he do this?