Humble Store have a WB Games Sale live right now which has a few nice Linux games going cheap, plus you can grab LEGO The Hobbit which works with Steam Play (ProtonDB has a bunch of "Platinum" rating entries for it) free for 48 hours. I gave it a brief run myself and sure enough, it works well.
As for the Linux native games on sale, here's what they have in it:
- Mad Max - 75% off
- Bastion - 75% off
- Middle-earth: Shadow of Mordor Game of the Year Edition - 50% off
If you have kids of your own, I can also recommend Scribblenauts Unlimited which works perfectly in Steam Play and it's also on sale.
Outside of the special WB Games Sale, Humble also have some other good Linux games going cheap like EVERSPACE (GOG & Steam keys included) at 70% off and Darkest Dungeon with 70% off. There's obviously plenty more than that.
Even if you don't pick up a game, LEGO The Hobbit free is still pretty sweet. It likely needs you to have an account open with Humble Store and I presume they will want you to be subscribed to their newsletter too.
See the WB Games Sale here.