Things that make games fun (I'll start)
sprites
Choices that change the world
Honestly, mostly who you play with. On the gameplay side, I like unexpected results.
Loot
A solid core gameplay mechanic that everything else builds off of like the portals in Portal or the idea of catching and battling pokemon in the original pokemon
I like meaningful equipment options, with various viable options (spec-ing into range vs melee VS tank etc)