2 games I regret:
Sinbad. First game I owned, and while I loved it, I had my newbie eyes on deeper, newer games. After going through a few different eras, I realized early SS is my sweet spot for owning and I actively sought one out again. Finally ended up with a second one in much better shape than my first.
Flash Gordon: one of my favorite games of all time, and I knew I would regret letting it go the moment the deal was offered. I got an amazing trade deal out of it so I couldn't refuse, but I've been looking for another in equal or better shape the instant it left. Just a fantastic effing game that I miss everyday.