Truth007: The vast majority of "drm free" games on steam are shovelware, even valve uses drm for most of their games. Also sometimes you have to jump through hoops to get it drm free like editing something,etc
That "editing something" means in most cases putting a string of numbers (the game ID) in a txt file.
For anyone who has ever modified autoexec.bat and config.sys files it is not even worth mentioning, as it only takes few seconds to do.
There are plenty of games on Steam that are lacking quality, to put it nicely, after they started accepting (almost) anything. That doesn't mean that the majority of their DRM-free games is garbage though.
They have tons of old games running on DOSbox, and all those games are DRM-free, if not as is, then after you copy those files to your own DOSbox. The same is true with all ScummVM games.
And as far as I'm aware of, all AGS games are DRM-free too, and if by some weird chance they would not be, the upcoming AGS support in ScummVM will fix that.
I don't have the first Half-Life games on Steam, but some people have told that even those are DRM-free, even though they are Valve's own games!
If you don't play the latest AAA games, there are quite literally thousands of DRM-free games on Steam, even if you exclude all freeware, tons of RPG Maker games, and all that.