A team of developers got a prerelease ROM which was rather unstable, patched all the issues, translated it into English, and now it is fully playable from start to end on any emulator supporting the Super FX chip. I have to say it was better than Star Fox 64 considering the limitations of the Super Famicom.
You can watch a video here: https://www.youtube.com/watch?v=PGqLwiVxTKY
Star Fox 2 has some interesting additions: it seems more fast paced than the first one, the ship can transform in certain levels (in Star Fox 64 a different vehicle would be deployed to the level rather than transform), there's Star Wolf and some new crew members that make some appearances in Star Fox 64.
FWIW, I played the patched ROM and it was pretty damn enjoyable. It's a pity they didn't release it, because it feels different enough from Star Fox 64 that I don't think it would have encroached on the other's release.