There are a few Nordic ruins that have incredible sights and are thoughtfully laid out, that being said, I prefer the Dwemer ruins.
After reading and learning about Dwemer lore, I just find them fascinating, especially with the addition of the Snow Elf questline in Dawnguard. The most advanced civilization on the planet just disappearing? It's mysteries like those that keep my mind occupied for hours, even after I've stopped playing. I will admit however, that the Falmer can be annoy enemies, along with their creepy Charrus pets, but it still doesn't detract from the actual Dwemer experience for me. Like someone mentioned earlier, you don't get the sense that you are walking through another tomb, and the dead are now back to life, you feel as if you are walking through what could have been a city, one filled with people, families, and children. There aren't any bones, no corpses, just what they left behind, and the husks of the once proud snow elves. Cool stuff.