The reviews are already pouring in for Dawnguard, most seem to be overwhelmingly positive (what did you expect?). I have read a few, including ones from Kotaku, and a great forum review on Kongregate. I think the best of the bunch so far though, has come from Redditor Jpagel, who offers nice, spoiler free insight to the new DLC, regarding new quest, wepons, and skill trees. Click the link below for the full read, but I think he summs up the DLC nicely below
Dawnguard is great. It’s large (I’ve spent about 20 hours in it so far) and it will definitely keep you busy in Skyrim again. Let’s face it, though – even if it were terrible, we would still all buy it just because it’s more Skyrim. If you’re on the fence about buying it, let me give you a little nudge: buy it. There are new shouts, new abilities, new quests, more achievement points, and MUCH more gameplay.
Man, this cannot come out for the PS3 soon enough!