I believe this is something to be aware of and if this is something you don’t want use GOG instead. But in reality as long as Steam exists you will be able to download and play your games. If Steam ceases to exists then you will not be able to download them, but there will be ways to still play them, if you previously downloaded them. It is not like “owning” movies on Amazon (or just recently on the Playstation Store), where you always need to stream the movies.

Valve, by a far stretch. Also they support their games for a long time. Sadly they don’t make as much games as they could, because of the money printing machine that is Steam.

Definitely check out OpenGOAL. It is the best version to play right now (even better than the remasters for PS3/4). It is basically a native port for Windows and Linux.

https://opengoal.dev

Half life 1 also! May be the graphics are a bit dated, but for that is the Black Mesa verdion