"Cryostasis: Sleep of Reason" is an interesting game that is also not being sold on Steam anymore.
If we're also talking about the GTA games, didn't they cut the music from some of them due to licensing issues?
So essentially some of the digital GTA games are inferior versions now.
Here is a list of games that have been removed from the Steam store:
https://steam-tracker.com/apps/delisted
Quite a lenghty one. Chrome and Chrome: Specforce are two of the ones I remember.
They were not...particularly great games back in the day, but I still remember them being more like a tech-demo with bad gameplay added on top.
Some of the Ford Racing and Duke Nukem games are also gone.