Today through Sunday, May 4 on Steam, Image & Form's SteamWorld Dig is half price.
I've had plenty of good things to say about this game in the past and I stand by it. It's got that Mr. Driller-style gameplay that's a joy to play but with much more emphasis on platforming and there are even some light Metroid influences. All of that, wrapped in a robotic Wild West theme.
In addition to the discount, Image & Form has added the nine-song soundtrack to Steam, purchasable for $0.99. The studio also uploaded the album to its Soundcloud for quick listening.
If you played SteamWorld Dig on 3DS and liked it, consider double dipping.