Well the big three (Morrowind, Oblivion, and Skyrim) all have parts that I absolutely love. Morrowind has the intricate story, bizarre yet colorful and well put-together world, and massive amounts of customization. Oblivion is the king of questlines, with awesome shit like the Thieves Guild and Dark Brotherhood (that mission in the mansion is so amazing). And Skyrim has the streamlined perk/skill system and most competent combat system, even if it doesn't have as many options as Morrowind. Combine them all and I honestly think you would have a close to perfect game.