I guess I shouldn't be so surprised by this entry after checking out your twitter and realising you're actually a professional pixel artist in the industry, but... even taking that into account, this is still pretty incredible, especially for a week.
It controls well, it plays well, it looks gorgeous, it's full of loving Giant Bomb references, and the soundtrack is great (and don't even get me started on that final battle!). I especially liked the slide invulnerability frames, which made the otherwise pretty hard single player much more accessible.
The whole thing is just a smart mix of Contra/Metal Slug and I would legitimately pay for a full-length version of a game built on this same framework. Well done!