Negatives:
Miraak is a potentially interesting antagonist that they never do anything with. The Dragon Cult remains thoroughly unexplored and underdeveloped. Restricting (almost) all the new spells to just one merchant is a bad design move, and the "implementation" of spears and werebears is something that seems purposefully designed to rub lemon juice in my eyes. Being unable to move your family to the house in Raven Rock is also annoying.
Positives:
Most characters are more memorable and likable than not. The environments are beautiful. Apocrypha and Herma-Mora are a delight. Very nice additions in terms of smithing, spells, enchantments, and alchemy. And honestly, I can't think of a quest in the DLC I actually didn't like, even if overall the MQ felt lacking to me.
Edit: So overall, I like Dragonborn, and at $10 (as part of Bethesda's "We're sorry we are so unbelievably bad at programming for the PS3" apology), I think I got my money's worth. I probably wouldn't have if I had paid the full $20 though.
Still, it ranks second in my overall favorite DLCs, behind Hearthfire but ahead of Dawnguard.