The Dark Brotherhood questline in Skyrim is definitely a standout for me too! The whole mysterious and dark atmosphere of the quests really immerses you in the world of assassins. The moral dilemmas you face along the way truly make you question your choices, adding depth to the overall experience. Another questline I really enjoy is the Thieves Guild questline. Sneaking around, pulling off heists, and restoring the guild to its former glory is so satisfying. The unique characters you meet and the challenges you overcome make it a memorable adventure. Skyrim really knows how to deliver captivating questlines that keep you hooked!