I play some Jhin from time to time and I always found him amazing to play, but never really understood what made him so good. I think there's 4 reasons for this:
1 - The mood around the champion is amazing, his quotes and ult music really give a special vibe.
2 - Versatility: From a full crit build to a lethality build he's never bad. Also he can just stack attack speed and crit and kite an ulting Sion, great in normals :D
3 - The skins are all good. Wish I had any, but I don't think any of his skins is bad. Maybe High Noon is a bit mediocre, but that's his worst.
4 - The guaranteed crit on the last shot. It sounds so satisfying and good and it really reminds me of old GP's q, how it sounded so amazing.