These additions, along with a 12-quest campaign, might sound like a lot of nice stuff for a DLC, and perhaps it is, but I felt underwhelmed. The first problem is that almost all of the additions are cosmetic. The Soul Cairn is an interesting place to visit, and Bethesda did a nice job in making it feel bleak and forlorn, but exploring it is no different than exploring anywhere else. Meanwhile, frost giants are the same as regular giants, coffins are the same as beds, crossbows are the same as bows, and so forth.
The other problem with the DLC is that its new big attraction, the ability to transform into a vampire lord, is worthless. Just like the werewolf form before it, unless you're level 20 or something, you're going to do way more damage and have way more options with your regular form than with either of the specialty forms, and so there isn't any reason to use them, except perhaps for role-playing purposes. Bethesda tried to make the forms more powerful by adding perk constellations to them (you gain perks by killing enemies while using the form), but even with the perks the forms are underpowered.
The campaign also has some problems. I already mentioned that the big decision you have to make doesn't change anything, but there are other issues as well. For example, I'm pretty sure the enemy you fight the most in the campaign is the falmer, which seems like an odd choice. The campaign also introduces an evil vampire named Harkon, but he spends 95% of the time off screen, and the only reason you decide he's evil is because of stuff you hear secondhand. Harkon doesn't actually do anything evil. He just hangs out in a castle. And finally, while the campaign is active, there are random vampire attacks in Skyrim's major cities. This is great for making it feel like there's really a vampire conflict going on, but the vampires far too easily kill named NPCs, including shopkeepers and quest givers, and so their attacks are more aggravating than anything else.
