Steam Labs is a virtual place where Valve conducts "experiments" aimed at making Steam easier to use. One of the most interesting experiments we've seen so far is the Interactive Recommender, which uses machine learning instead of conventional tags in order to find games you might be interested in.
The newest experiment, Play Next, performs a similar function, and is actually based on the same technology that powers the Interactive Recommender. But instead of rooting through the store to find games you might want to buy, it roots through your massive backlog (you have one, right?) to find games that it's about time you finally got around to playing.
The Play Next page lists three games from your library that you should maybe think about firing up next, each with a microtrailer (another Steam Labs experiment), tags, and a short list of similar games to give you an idea of why you might be interested. If you decide you know better than the machine, a "Next Picks" button will bring up a list of three different games. It's not clear if there's a hard limit on recommendations, or whether the number of suggestions will vary on things like the size of your library: I get a total of 12, beginning with Metro: Last Light Redux and ending with Shadow Warrior Classic Redux, before the list repeated.
Valve warned that there may be a few bumps along Recommendo Road as it continues to tweak and tune the system. "The algorithm we use for picking comparable games is also a new system we're experimenting with in this lab, and it's a work-in-progress. So don't be surprised if it sometimes shows you some unexpected comparison points," it wrote.
Most of suggestions I get are of the predictable, "Yeah yeah, I know" sort, but a few are unexpected—Jotun, for instance, is apparently akin to Shadow Warrior, Lovely Planet, and Limbo—and one (I don't want to name names, but it's the Thief reboot) just isn't going happen no matter how reasonable the recommendation—it's "similar to" Dishonored 2, Death of the Outsider, and Deus Ex: Mankind Divided—may be. (There are some things a machine just cannot fathom.)
The attentive among you may have noticed that Play Next is Steam Labs' experiment 008, and while the previous experiment, Community Recommendations, is 006. Valve said there's nothing weird going on: It started on Experiment 007 before Play Next, and it's still working on it.