A quote from Scott Sharkey sells this the best:
A really simple Wolfenstein 3D clone probably wouldn't be worth getting fired over. 8bit Killer, however, is a lovingly polished game that makes subtle visual and aural homage to just about every game in the NES pantheon. It's a completely original production, free of tacky sprite rips or other easy shots at nostalgia. Instead, the game makes strong artistic and musical hints at everything from Contra to Bionic Commando while remaining something completely different.