I think a remake would be awesome. The atmosphere of the game wouldn't really go away, I don't think. Metroid II was freaky because everything was really dark, and alien - the ambushes could be re-adjusted so they're still freaky with a bigger screen. I think this would probably be more suited to being one of the last GBA titles rather than a DS game. (The DS would try to introduce too many novel game concepts. I'm guessing someone would attempt to incorporate the stylus, which would be REALLY out of place in this game.) Also, 2D on the DS isn't much better than on the GBA. I think the primary problem would be if more backstory than makes sense was inserted, or if there was extra areas a-la Zero Mission. (On ZM this was fine, due to retconning stuff from Super Metroid in, whereas on Metroid II this would be catastrophic for the most part, areas in Metroid II had no names, no defining characteristic. You just kept going deeper and deeper into the abyss. I don't think Metroid II had anything to do with the GB's limitations, but the small screen did help them surprise you with Metroids.
Ideally, this would involve minimal changes to the areas, just a lot nicer sound (same sounds, music/new versions... no new music) and visuals... some nice backgrounds and more detailed environments.
Ideally, this would involve minimal changes to the areas, just a lot nicer sound (same sounds, music/new versions... no new music) and visuals... some nice backgrounds and more detailed environments.