Right at the start? Liszt's transcription of the Liebestod from Wagner's Tristan & Isolde (S 447).Score here.
Thank you! Those few seconds of music were so immediately captivating that I just had to hear more, and that doesn't happen to me very often with Liszt.
To be fair, the captivation probably owes a bit to Wagner. Try the originalOr better still, listen to the whole opera!