Insanely Twisted Shadow Planet, according to the ESRB. The organization has posted a PC rating for the title, which was then noted in an article on ExtraGuy. Said article was subsequently tweeted by the Shadow Planet account with a "hmmmmmm" and a winky-face.
A winky-face. Yeah, we'd say Insanely Twisted Shadow Planet is definitely headed to PC. We've contacted developer Fuelcell Games just in case.