If Mega Man 9 isn't retro enough for you, you might enjoy the enormous, jagged pixels found in the Atari 2600 demo version of Mega Man created for 2007's I Am 8-Bit show. David Galloway has finally released the demo on Atari Age's forum, which means that you can download the game and play it on an Atari 2600 emulator right now.
The brief demo is an impressively faithful translation of the NES game's mechanics, with Mega Man running, jumping and shooting just as you'd expect (though shooting is mapped to down on the joystick, because the 2600 only has one button). The demake ends at the Elec Man fight, which is even harder in this version than it is in the original. A playthrough of the entire demo follows after the break.