Brian Provinciano's Retro City Rampage is a 2D sandbox kill-em-up similar to the pre-3D GTA outings—but with more 1980s. Available for pre-order, it'll be released on PC in both DRM-free form and on Steam, and on PlayStation 3, PS Vita, Xbox LIVE Arcade, and WiiWare. The distinctive soundtrack may already be bought separately for anyone liking the cut of its chippish jib.
Update: Good lord, in development for 8 years. Cory blogged it in 2004!