I think that nostalgia is the reason why I've been so excited over the PlayStation Classic. The Dreamcast is my favorite system of all time, but I discovered a lot of affordable hidden gems for the PlayStation right around the time that the PlayStation 2 came out. I remember going to GameStop and video rental stores and buying large quantities of used PlayStation games when they became dirt cheap. I still have all of them now.
Obviously, the 2D games have aged much better than the 3D games at this point, but with all the shmups, RPGs, platformers, and puzzle games on this system, the PlayStation Classic provides a really great opportunity to discover some really cool games that you might have otherwise missed.
If you're not familiar with the PlayStation library, there's a lot more to play on it than the usual titles that everyone suggests. This is a link to one of my all-time favorite articles about the PlayStation's hidden gems on Racketboy's website.
http://www.racketboy.com/retro/best-undiscovered-playstation-ps1-psx