Seriously, I don't get it why some people are disappointed by Dawnguard. I currently play it for my 2nd time and it's just great. Besides some unique and beautiful places like Fort Dawnguard, Castle Volkihar, the Soul Cairn or last but not least the outstanding Forgotten Vale, you get two whole new skill trees (Vampire / Were Wolf), an interesting story, a great follower (Serana) and some nice loot. In addition, it's really well-made, even if compared to Dragonborn. I like Dragonborn too, probably better than Dawnguard because of the massive amount of loot, but nevertheless Dawnguard is just great.
It all comes down to the price I guess. Yes, it's arguable if it's worth 15 bucks. But my opinion in this matter is the following: Nowadays, all DLC's are that much expensive. So if you compare Dawnguard to DLC's from other games, which are much shorter, than no way that Dawnguard is (was) too expensive. And if you look at Skyrim as one game (including the DLC's), can anybody really complain about its worth? Seriously, most of us spent about 100 bucks for the game including the DLC's, and what did we get? A masterpiece or at least a very good game with a playtime between 150-3000 hours. I rarely know games with such a good cost-benefit-equation.
Your opinion about Dawnguard?