Dawnguard is the first massive expansion pack for the Skyrim epic. A lengthy quest and a spate of new powers is always appreciated. Given the history of Elder Scrolls expansion sets (Shivering Isles is still one of the truly great add-ons), where does Dawnguard rank?
Well, for starters, it isn't up to par with the best questlines in the game. It's not as solid as Dark Brotherhood or the Civil War --- but it is better than the others. It isn't as repetitive as the Thieves Guild and is worlds better than the rest, including the main storyline. Giving you an actual benefit to being a vampire (it was little more than a major annoyance in the main game) is nice and the vampire lord powers can get impressive as you level them up. Ditto the werewolf powers, which end up being stronger and more useful as time goes on.
The other major addition is a new type of dragon --- the Legendary dragon. They only appear when you have nearly maxed out your level (I found none before level 81) and they are a bit of a bitch to kill but give some really, really nice loot.
You want to be rather powerful before taking these missions on, and they will make you significantly stronger. I have to wonder where they can go next without introducing new powers because, as it stands, I don't know what boss can actually cause problems right now. The game isn't designed for raiding, so that option doesn't exist.
Dawnguard is worth playing. It will improve a lot of things. It's just not as good as the highest points of the game --- but expecting that in DLC is expecting a bit much.