Playing a pacifist was some of the most fun I've ever had in Skyrim. Taking the main element of the game—killing your enemies—away leaves you with an entirely different game to play. It forces you to think of other ways around obstacles and to focus more on non-combative skills than you usually would. To play a pacifist, you must follow three rules:
1. Don't kill anything, ever.
2. Don't employ followers or summons to kill anything for you.
3. Don't use fury spells to force enemies to kill each other.
Since that wasn't difficult enough, I also gave myself some other limitations with this character, who was a Khajiit. I played into the lore of Khajiit not being permitted in cities by not allowing him to barter with regular merchants—only Khajiit caravans, Thieves Guild fences, and scholars at the College of Winterhold. He was also obsessed with fish and absolutely had to steal every piece of fish he saw, whether or not he could actually get away with it, though figuring out how to get away with it was sometimes a great puzzle. I also didn't fast travel anywhere.
The beauty of Skyrim is that you really can mold the game how you see fit. You can give yourself whatever limitations you want to make it more challenging and more interesting.
