For Zoo Tycoon, I've only played the demo once, and that was a few years ago.
For Roller Coaster Tycoon, I've played all three versions and the expansion packs to all three of them (I still have them laying around somewhere). I always enjoyed playing that game as a kid. Now that I would have a better idea of how to properly play it, I would like to get back to playing it, but I doubt I would have the time to do so.