The soul cairn is what sovngarde should have been if you asked me(maybe a bit darker). about 5 or 6 quests to do in the place alone, a dead shopkeeper who sells you decent tomes and equipment for soul husks(plat things that grow around the place), soul crevises and portals, puzzles requiring the use of magic, and even brand new enemies that are each unique in their own way.
Plus, the spell summon Arvak is definitely useful if you can get it from here. Who wouldn't want an undead horse to call forth whenever you want?(especially with the addition of horse combat

).
And whats even better, you can return here after the questline is complete! This fact alone makes it twice a good as sovngarde.