All the time. Though I play the newest ones too. I jump back and fourth between every generation of pokemon all the time. It's probably my favorite game series and I find a lot of comfort in casually playing through the games again. I also shiny hunt which is easy to lose track of time with. Pokemon Crystal is probably my most played game in all my time gaming. I have played this game off and on for over 20 years now.
Pokemon Mystery Dungeon: Explorers of Sky. It's one of my favourite games of all time.
I don't play it often, but it's something I savour when I do.
Explorers of Sky is packed with content, it has a bouncy, adventurous and emotional soundtrack, and it delivers on some imaginative, highly detailed pixel artwork for the DS. The story is very engaging and ambitious too, especially given that it's a spin-off Pokemon game on a handheld console.
If you haven't played it already, I highly recommend it.
I never felt like getting into emulation or retro to play them and the new stuff is not my thing. Although I can't honestly say that I would enjoy them very much anymore without a core group of friends to compare Pokemon to and the like.
I could never get into the older Pokemon games even though I tried to do so. I always remember trying and my brothers were heavily into the games but they never took the time out to help me play and understand.