A purchase gets you 11 levels today and access to the remaining 22 in the final release.
The retro-FPS Dusk, as we said in our preview earlier this week, is "not shy about its Quake-and-Doom inspiration." It's fast, bloody, loud (Brutal Doom composer Andrew Hulshult created the soundtrack), and looks (and plays) like it fell out a rupture in the space-time continuum that leads directly back to 1994. It is also, with very little fanfare, now available for pre-purchase on Steam.
Dusk, like Doom, will ultimately offer 33 levels spread over three episodes, the first of which, "The Foothills," is playable now. One of three "Endless" survival mode arenas is also in there, if you just want to run around and shoot stuff until you die, without worrying about... well, anything else at all, really. Multiplayer doesn't appear to be live yet, but it's on the way as well. It goes for $20/£15/€20.