Hello! We are excited to announce Steam Families, available today in the Steam Beta Client. Steam Families is a collection of new and existing family-related features. It replaces both Steam Family Sharing and Steam Family View, giving you a single location to manage which games your family can acce...
As far as I know, it's mainly games with DRM that might trigger on multiple installs/computers. So companies will disable family sharing. Not sure how common this is.
I used to use old (current before the update hits stable) family sharing and I'd say among 250 games, at least more than 220-230 were available on family sharing. This included MGSV:PP and Max Max back when they were released. I don't know if developers become more restrictive on family sharing over the years, but seeing that old designations will carry on to the new Steam Family thing, I reckon this will be a huge hit in the age of crackdown on password sharing in other media platforms.
We have 1278 paid games that are included and 55 that are excluded from family sharing. Seemed to be mostly ubi, rockstar and ea games. Games that you claimed while they had a limited 100% discount are also excluded. The last few are live-service or mmo games.
"Family sharing" is now a feature listed on every store page. Same place as singleplayer, trading cards, cloud saves and similar.
As far as I know no major changes has happened in which games support it, but that may change now that sharing gets more attention.