If rumor is to be believed, the next Valve game might look something like this.
PC Gamer recently snapped some pictures of the concept art while on a tour of Valve's office, and while they've since been removed from the PC Gamer site, the images live on in the various corners of the Internet. You can find some of them over at The Escapist, and none of them look like they fit with any of Valve’s existing franchises.
The pictures depict an assortment of futuristic individuals. There's one woman who seems to be missing a nose, another person with wooden/metal legs, and a few of the girls appear to be pregnant. Most of these people definitely look like aliens, and the futuristic gun (at least, I think it’s a gun) also looks extremely cool.
At the moment, however, there’s no way to know what kind of project this is. It might be concept art for the next Half-Life, or it might it might be something that gets scrapped before it moves beyond of the planning stages. My guess, though, is that we're seeing something totally new from Valve.