Gamasutra has a great interview with Mega Man 9 producer Hironobu Takeshita about the development process behind the forthcoming downloadable platformer. The dev team has attempted to make the game as true to its NES roots as possible, complete with simple visuals and 4bit sound. Takeshita-san says that the designers even included graphical bugs including flickering to simulate a NES processor's inability to draw more than three or four sprites at once.
It's an interesting exercise, and the sort of thing that could perhaps only happen via PSN, Wiiware and/or XBLA, where the overheads are low enough to allow experimentation. It's also telling that this is not a pure 'simulation', the game is too large to fit on a genuine NES cart - it's a modern interpretation, similar to the way artists like Ladytron and John Vanderslice use vintage hardware to make entirely contemporary music.
So what other 8bit games would you like to see rebooted in this way?