Morrowind is hands down the best elder scrolls. If you want a TRUE sandbox where you can do whatever the hell you want, that’s your game. Some issues include graphics, no quest markers (you have to read the quests and follow directions), the leveling system is not intuitive at all, and combat is heavily stats based.

Upsides are you can craft any spell or enchanted item using any spell effects you know. Ring of permanent invisibility. Spell of lock every door within 50 feet. Summon 3 different daedra at once. Conjure a whole set of bound armor. Explode yourself in fire. Literally anything.

The elder scrolls renewal project is working on recreating morrowind with skyrims engine and I really hope it comes out soon.