NES Hydlide, utter garbage. That was my view of the game back in the 80's when I first played it, still my view after trying to play it again in an emulator ~20 years later. Unplayable is another word that comes to mind.

Genesis Super Hydlide, for some reason I took a chance on this one even after the terrible NES one, and I was really glad I did. It's definitely got a steep learning curve, but once you start figuring out things like "don't kill everything that moves" so your karma or rep or whatever doesn't plummet, it's a surprisingly deep game for its time. Make sure to get the money changer early as possible. I mean wow, even money can wind up weighing you down in this game. Also, I have to say, some of the best music on the Genesis is in this game. Really great stuff, and in a style not really heard much in games of its time. Sometimes I would plug in the cart just to run over to the sound test cave and listen to the tunes. Graphics are kinda crap, though.

Saturn Virtual Hydlide, don't remember much, haven't played it since it was new and I rented it, but it was definitely not a good experience.