The greatest action-RPG on the NES, that's right, even better than Legend of Zelda.
Crystalis follows the adventure of a warrior sent from the future. He is sent back in time to stop an evil and very powerful dictator from taking over the world before he gains his full power in the past. The game begins with you waking up from your time machine in the past and emerging from the cave it is housed in and into a small village. It is in that small village that your adventure begins. You will battle many monsters and minions and their powerful masters in your quest to rid the world of this great evil.
The game is very impressive, graphically, for an NES game. The sound is just as impressive. There are a number of areas, dungeons, caves, and towns to explore. Unlike Legend of Zelda, there are also a number of NPCs to interact with as well as storyline that you can follow. Another improvement over Legend of Zelda is the ability to level-up your character. You can gain sword and armor upgrades like in Zelda, but alongside that you still get the character level-ups; making the game that much more satisfying in the end. The game is also a bit more challenging in the later areas of the game than Zelda ever was.
So if you're a fan of the original Legend of Zelda, you must check out this game. It is well worth it's price and your time.