There was an interesting fan project which had the goal of replacing all the low-res textures in the game with high resolution textures. From the few screenshots that were released, doing so makes a great difference in the graphical quality of the game.
Sadly, I'm looking at the website now and I see it hasn't been updated in several years, so it doesn't look like this project is going anywhere...
http://sidney.fwheel.net/GK3RP/
