i still have this game and though i never beat it, i still loved it..
its sorta like Metroid come to think of it.. you ride around in this tank type vehicle, over all sorts of terrain (including diving underwater i think) but you can also hop out and crawl into areas that your tank couldnt fit in to. Ever play that Ninja Turtles game for the NES (turtles 2??) that has some side scrolling mixed with overhead gameplay? Similar to that i'd say. Alll i remember is your character having a huge head (lol) and the first boss being this giant slime...
and that i had a book based on this game, which i read, and if the story of the book is anything like the story of the game.. you're trying to rescure your... pet frog!?
I might have to pickthis game up. its one of those NES games i got later on in life, that i enjoyed but due to my NES's bad connection, was never able to finish because the games would lock up.