Do you like RPGs? More specifically, action RPGs? If so, you will want Planescape and Baldur's Gate (I recommend both 1 & 2, but some people will argue only one or the other, in which case I kind of prefer the latter as a game but the former as a story). Also, I like you played "a little Myst" when I was a kid, and only recently played both Myst and Riven and loved them, so take that as you will.
With GOG you can download and redownload whenever you want. It's kind of like Steam, but without any sort of program to frame it all, just an account on their website. Also, you download the installation files, so if you wanted to, say, temporarily store them or back them up on some kind of portable memory/hard drive, that's an option.