This game is totally awesome. There's no denying how much fun it was to play Greedy Guns. I definitely was getting a Metal Slug vibe the entire time, and it most certainly has shades of Metroidvania.
If you've got the money, I'd recommend supporting the Kickstarter. It's definitely a game you'll want to buy at launch.
Only gripe I have: no Gamecube Controller Adapter support. :(