An excellent remake of the first two megami tensei games for the NES. If you're going to play them, then play this remake because it actually has an in-game map.
KMT1 is pretty simple, it's a series of interconnected dungeons with bosses to beat, and some items to find if you want to make the bosses beatable at all, it's a bit like a DnD campaign in a dungeon crawler form.
KMT2 is an entire proper post-apocalyptic jRPG where you and your friend leave the safety of your shelter to face the demon filled Tokyo outside.