Interesting thing about fan-hacks like this is that they actually don't do anything that the NES wasn't capable of, there are a few fanhacks that made it to physical form and can be played on an NES. Anyway this is a Megaman 4 fanhack which is basically bullet-hell Megaman, but it has some really cool ideas, special effects, and clever tricks I didn't think would have been possible on the old NES.
42:40 Wiley stage is impressive
1:02:40 The final boss section is just absurd