I have tested games EXTENSIVELY in the Steam for ChromeOS beta. It's not a powerhouse for modern gaming, but there are many games that run well from up to the 7th console gen. Of course Source engine games run well, but Unreal engine 3 games run solidly too. The hardest that I have pushed it is Dark Souls 3, which doesn't run well, even at the lowest settings (15-40fps), but is stable, which impressed me. 720p 60 is possible across a large variety of games, but 900p 45 is what I am usually shooting for. Bayonetta, Bulletstorm:FCE, DMC, all of the Nightdive remasters, Vanquish, Arkham Asylum, Prodeus, both Portals, Enslaved, and Prototype 2 have all run very well.
Steam is now also available on Chromebooks. But the software is still in its beta stage. We installed Steam on an Asus Chromebook Flip CX5 to test out how well the program runs right now and found that some well-known games in our Steam library are playable on this Chromebook.