It seems appropriate to spell out my viewpoint at the very start of this. I not only look at this game with a certain nostalgia, but as a player old enough for their formative gaming experiences to have been 8-bit, and that includes having played Crystalis when it first came out.
Still, in contrast with other old games to which I returned only to find memory overly kind (picking up the original Dragon Warrior again, I was annoyed to find that I had to select "STAIRS" from a menu when I wanted to go up or down a floor), Crystalis held up very well a long time afterward, on multiple levels.
One of these was its world-building and storyline--arguably, more appealingly and lavishly developed than in any other 8-bit game of the type. Not only did the graphics make the most of that era's capacities in presenting a colorful, varied world. The main thread of the game takes place within a bigger, more dynamic narrative--a larger struggle against the Draygonia Empire. This facilitates the presentation of an array of engaging NPCs (developed enough to be capable of different responses depending on the situation, and even to display a measure of humor), mini-quests well-integrated into the larger drama (like the rescue of the villagers from Leaf), and dramatic plot twists (our hero is not the only one on a quest here), while more broadly imbuing the adventure with the feel of an epic, accentuated by a memorable musical score. It also has an abundance of appealing features, not least in the battery of magic spells the hero acquires (which permit everything from telepathic connections, to the power to disguise himself with an enchantment--both of which are essential to his successfully completing his missions).
It helps, too, that the gameplay is relatively smooth. This is most obviously the case in the quality of the controls, particularly where the management of a large and diverse stock of weapons, items and spells are concerned, and also the navigation of that world the game provides. (Using a pair of cheap warp boots, or teleportation magic, one can easily zip about the world map rather than having to walk all the way.) However, this is also the case with the unfolding of the larger quest. Where, for example, in Zelda II: The Adventure of Link (the game with which Crystalis is most frequently compared), it has fewer frustrating patches. There is nothing quite like, for example, the journey through Death Mountain to acquire the Hammer, or from the North Palace to the final palace--sequences which are difficult not because they offer up clever new problems, but because they simply require Link to go through a very long version of an already familiar environment without having a chance to conveniently heal himself, or save his progress, making for a grueling course one has to repeatedly attempt before success, drawing things out. Rather on those few occasions when I found myself getting stuck in Crystalis, it was a matter of the more cerebral challenges--as with unmasking the identity of a certain monarch through the use of a certain magic spell.
Of course, some have said that the game goes too far in that respect. The need to switch between different swords to defeat particular enemies apart, one can get through the fighting on the strength of button-mashing. Perhaps a bigger issue is that it is not a particularly lengthy game, even by 8-bit standards. Even while playing at a leisurely pace, leveling up well past where I needed to be at any one point, and preferring to chat with every villager, try every possible way through every maze, and puzzle things out when I got stuck rather than rush to the guides, I played through in about fifteen hours (a fraction of what the original Final Fantasy promised). A player less committed to such an approach to the game (or simply more skillful) could easily shave some hours off of that.
Still, button-mashing can be just the thing when one is looking to relax, and if there are longer games, this one was certainly fun to play through again--and, while the game does not seem likely to get much better known any time soon, thoroughly earns the esteem in which it is held by most of those fortunate enough to have encountered it.