It is hard to tell since you never have access to the code. For me those are the games that don't have errors, saves from older versions are compatible, RPGM games don't stuck if you "overclick" them, no delay when switching rooms (on opening the door). Some mini-games inside. A lot of customization in the UI (while this is simple, not a lot of devs do it). While Unity is capable of way greater games than RenPy and RPGM, people still use the same stuff to make another BB clone.