I hate to say the obvious but it depends on what games YOU like. Find the full list online and run your eyes down it, there are soo many on there. A lot of fodder though.
I've downloaded Vampyr from it, which is meant to be pretty good. I always keep my subscription going as there are always things on there I want to play.
I've been playing Hitman after recently getting gamespass, quite good, loads of different various ways to do the missions which keeps it fresh and interesting.