white bread with butter on for the most part, dawnguard suffers from everything skyrim does - cool lore at points peppered throughout mediocre gameplay, utterly flavourless and bland characters, and dungeons that go on for too long.
what "story" there is is basically non-existant. it's vampire hunters looking for vampires and the inciting incident to start you off as a vampire hunter is... someone asks you if you want to be one? there's all this faff about harkon's prophecy but he doesnt actually do anything for the entire thing. he is literally just in his house doing fuck all! you go through these mad events, like going to the soul cairn and finding auriel's bow and the last snow elf to stop harkon, who really we have been given no reason to believe he's actually anything more dangerous than a pretty tough vampire? serana is one of the most popular skyrim companions but she's also a glass of milk on a cold day. laura bailey is a great voice actress but even she comes across so wooden here. isben? i get it, he's stubborn and a bit extreme. do they do anything with this? of course not, isben doesnt actually DO anything. his unorthodox methods are never shown, explained, or explored. so he ends up being a kind of rude man. castle dawnstar is the biggest castle in all of skyrim and like, for what? its a hassle to walk around and about 6 people live there. i think the dawnguard stuff taking place IN skyrim also sort of blows because it doesnt really feel all that different to the base game. you're still fighting falmer, going through dwemer ruins and that jazz. its boring
the stuff thats good about dawnguard are its lore. so much of skyrims problem is that there are good and interesting pieces of cool fantasy and magic and theyre so hard to access between the miasma of boring slop and bad writing. but then you find the moth priest and he talks about how he is part of a tiny order of scholars who study the otherwordly titular elder scrolls, and there are these magic moths that help one see, and how he's gone blind from reading the scrolls. you also go to the soul cairn and hear about the "ideal masters", these unknowable beings that gather mortal souls for some unknown purpose, and live over an underdead lightning realm. you meet the last snow elf and hear about the history of the falmer and how they were blinded by a faustian bargain with the dwemer, themselves long dead, and so the falmer are trapped blind and insane. that stuff is so cool! it desperately left me wanting for more mystery, more lovecraftian horror with actual characters who have motives and perspectives and feeling, instead of the perfectly digestible slop we got. dawnguard is fine. its a butter sandwich, water soup, ready salted crisps, etc etc