I've replayed Dragonborn more times than I'd care to admit, and every time I take that boat from Windhelm to Raven Rock I feel like I'm landing in an actual place rather than a content drop. So here's my tour of Solstheim, the Miraak business, the Black Books, and the bonemold-and-mushroom flavour that, for my money, makes this the best thing Bethesda bolted onto Skyrim.
Getting there and reading the island
You trigger the DLC once you've absorbed your first dragon soul. Cultists ambush you with a note marked for "the false Dragonborn," and following that thread points you at Northern Maiden in Windhelm docks. Captain Gjalund grumbles, takes your coin, and you're off.
Solstheim is the clever bit. Half the island is grey, ash-choked Morrowind, with House Redoran rebuilding Raven Rock around an ebony mine; the other half is snowbound Nordic country with barrows, Skaal hunters, and Stalhrim. Tonal whiplash, on purpose. The Red Mountain eruption from the events around 4E 5 reshaped this place, and the ash everywhere is the receipt. Watch for ash spawns and the genuinely nasty ash hoppers in the south. And look up, because that floating spectral tower you can't reach yet is the Temple of Miraak, the whole point of the DLC.
The Miraak arc
Miraak's the hook: the first Dragonborn, who learned the Thu'um straight from the dragons during their cult-rule and then turned on his masters. He's been squatting in Apocrypha for an age, slowly reaching back into the world. You'll find Solstheim's people building his temple in a trance, chanting "we all fall before the Dragonborn," and you spend the campaign breaking that hold and chasing him through Hermaeus Mora's realm.
The Skaal questline weaves through it. Storn Crag-Strider, Frea, and the village give you the lore and the stakes, and there's a real gut-punch at the climax involving Mora's price for knowledge. I won't spoil exactly how it lands, but it's one of the few quests in Skyrim where the cost actually feels like a cost. The final showdown lets you fight Dragonborn-to-Dragonborn, Bend Will and all.
Black Books and Apocrypha
The Black Books are the real treasure, and you should grab every one (seven total). Each yanks you into Apocrypha, green-black corridors of stacked tomes, lurking seekers and lurkers, tentacles everywhere, and at the end you pick one of a few permanent powers, swappable later by re-reading the book. Standouts: Secret of Strength (power attacks cost less stamina), Secret of Protection (halve physical damage at the cost of a stamina drain), and Black Market, which lets you summon a merchant anywhere. Absurdly handy mid-dungeon. Waking Dreams is the campaign book; the rest are scattered in dungeons across the island, a couple gated behind quests.
Then there are the three new shouts: Bend Will (tame a dragon to ride it, plus solve the Wind Stones), Dragon Aspect, and the Black-Book-taught Cyclone. Riding a dragon is more novelty than war-winner, but doing it once is mandatory fun.
The flavour that sells it
What I keep coming back to is the texture. Bonemold and chitin armour are back, Morrowind crafting styles you can actually forge. There's a Telvanni wizard, Master Neloth, who is gloriously rude and runs a mushroom-tower at Tel Mithryn that grows rather than gets built. Riekling camps, the Dwemer ruin Kagrumez with its resonance-gem puzzles, ebony ore, Stalhrim smithing, new ingredients like ash yams and Netch jelly. It's dense.
And that's my closing thought, which is also the brief I set myself. Raven Rock has maybe twenty named NPCs and I can tell you what most of them want. The disgraced mine, the Redoran councillor, the Morag Tong assassin lurking in the past. Compare that to half the Hold capitals on the mainland, where I'd struggle to name three people. So: why does Solstheim feel more alive than most of Skyrim proper. Is it just the smaller, hand-tended scope, the Morrowind nostalgia doing the heavy lifting, or did Bethesda simply write these people with more care because there were fewer of them?