There's way too much stuff in there, but as of right now I think it's Mechanicus, and the Serious Sam HD remasters, thanks to a recommendation in another thread just now. I also have a couple interesting demos I downloaded. The problem is, I haven't played anything from my Steam at all in the past month or so. Everything I've been gaming has been outside of it.

Also hilariously, these Serious Sam games were the literal first games I bought when I created my Steam account and I never played through them. They were an impulse buy from a friend's recommendation back in the day but I wasn't as into boomer shooters as I am now.