I didn't like Mockingjay that much either. I really liked the ending, though, thought it was lovely. But the book itself didn't grab me the way the other two did, and I'm sure it's because the scope got too big for the POV. The first two books benefited from Katniss's limited POV because they were essentially self-contained and the action was extremely focused both geographically and in number of characters. Mockingjay opened the whole thing up and got huge and unwieldy...
But I'm trying to reread them now so maybe my thoughts will be refined if I manage to push myself through it again.