I would have a difficult time choosing a single favorite video game, but I don't know that I've ever enjoyed another game more than Crystalis.
I discovered Crystalis in an attempt to buy Ultima: Exodus. Ultima was only $15 and I had heard good things about the series. My copy turned out to be defective, so I exchanged it. That copy was defective as well. After my third defective copy, I decided to try something else. Crystalis looked interesting, and was also $15. The price and tbe cover art convinced me to take a chance on it, and I soon learned that the cheapest game in the store can be the best one. (I never did play either of the NES Ultima games.)
Other video games have occupied my thoughts and influenced my drawings, but few to the extent that this one did.
SNK did not produce many other games for the NES. In later years, I hoped to find another comparable action RPG. The closest I found was The Legend of Zelda: a Link to the Past. That was a very good game, but I never found another Crystalis.
There were no such guides back when I played Crystalis, but today you can find a good one at Mike's RPG Center.
And if you'd like to play the game on a modern platform, it's included in the SNK 40th Anniversary Collection.