so far only found 1 game not working on dstwo (kirby mass attack or something) the eu version doesn't work but the usa does (or is the us that doesn't work, i dont remember, the thing is only one region of that game is not working, so you can still play the other version which is exactly the same thing)
either way, almost every game works, it would help if you got a list of games that you wanted to play, so peoeple can tell you if they work
inb4 pokemon works 100%