All the ID Software stuff worked ( eg. DOOM, Quake ) but outside of them and Loki, not a lot of commercial stuff. And I don’t think the Loki catalogue was very current or extensive.
There were lots of Linux native games but they were much more primitive ( though not necessarily less fun ) like Tux Racer and Pingus. There were also adventure games.
There was also a thriving game engine “clone” scene, especially for Blizzard stuff. Not all of it ever really got there in terms of features or quality. These were designed to work with the “assets” from actual commercial games. There was Stargus for Warcraft and StarCraft for example. There is DevilutionX for Diablo which is great. Often there were fully open source games built off these same engines ( BosWars? ).
By the standards of today, the Linux gaming scene would have seemed pretty shitty. You were not playing the same AAA titles as your Windows friends. However, if you were a Linux enthusiast, there were plenty of really fun options to keep you entertained.
I think Linux has always been a bit better off than Mac with regards to gaming.
[ Edit: Memory correction - DevilutionX is way more recent. Even Stargus did not appear until 1998 as did Pingus. Tux Racer was not until 2000. Loki was a 1999 thing too. So, my comments above are perhaps more valid for 1998 - 2005 than 1991 - 1998. DOOM was 1994 at least and Quake was 1996. ]