I loved Oblivion. It was like Morrowind lite.

I really loved being able to create my own spells at the Mage's Guild.

Everything more memorable than Skyrim to me, because it feels far more alien. Far more like it's another world. No offense to Skyrim. I've played the heck out of it, enough to the point where I got to 2 shot the Ebony Warrior w/o sneak attacks (and also the weird Ancient/Legendary dragons or w/e). It's just that with shouts and dragons dominating everything, even if they are Elder Scrolls flavored, makes it seem almost generic by comparison.

Walking upon the invisible town, for which one mage is responsible.

Finding a Lich in the basement of the house you just bought relatively cheaply!

The Knights of the Nine with the Pelinal and Umaril lore.

The Mage's Guild joining quest where a teacher had been killing prospective mages by way of a ring enchanted to weigh 300 pounds only upon being picked up. Put it in the well. They go to get it, at his request, and drown.

Manimarco and the creation of Black Soul gems.

Dark Brotherhood having you kill the inmate who mocked you at the start of the game!

The Gladiatorial Arena first pitting you against other people. Then rigged matches to try and kill you. Then just monsters, because no person in their right mind wants to fight you anymore.

Dark Seducers make my heart DOKI DOKI

CHEESE FOR EVERYONE! No, scratch that, cheese for no one.

Haskill.

I still remember the sheer sense of wonder I got when I entered the Shivering Isles. The house around you and Haskill turns into myriad moths or butterflies, and if it's night time, the sky there is a beautiful violet star scape. It really felt like walking into another reality.