i have blue, yellow, gold, silver, crystal (my first pokemon game!!), ruby (the first i actually finished!!), emerald (which i still haven't finished, omg), leafgreen, diamond, platinum, heartgold, white, white 2, x, and omega ruby!! \o/
I have them all, save for the original Japanese versions. They all still work, too. The only issue is sometimes the older games [red, blue, gold, silver...] their batteries die out and I have to replace them manually. Sometimes it can be a pain, but generally speaking I don't really mind doing it.
If you haven't played a Mystery Dungeon game, go out and get one! I'm all about the generation games, but Mystery Dungeon is the best spin off game I have ever played. I got Explorers of Sky after playing diamond in 4th grade, and I wasn't sure if I was gonna like it. I loved it. Super challenging and honestly just fun.