I'm just getting started on this, following this as a guide
http://noelberry.ca/nes on hardware limitations, and going for some extended features with MMC5 chip (making 16,384 different tiles available per screen rather than only 256, and allowing each individual 8x8-pixel background tile to have its own color assignment instead of being restricted to one color set per 2x2 tile group)
The waves infront of the posts here are sprites.
The only unfaithful constraint is that I can't pull tiles from rom and colour them on the fly, so tilesheets will probably be larger with duplicates to emulate palette shifting.
Here's a shot of the game running, some videos here:
http://hawkenking.tumblr.com/

(the green waves in this sheet is just for reference in the editor, those are swapped out)
The pirate sprite uses 2 palettes which probably isn't going to leave much variation for other sprites.
Any feedback or complains about me not being pure enough are gladly received!