I have often seen Crystalis called a Zelda II clone.
While The Adventure of Link remains a favorite of mine from the NES era, the claim strikes me as simplistic.
The player's experience of the worlds of these two games seems a logical place to begin the comparison. Where Zelda shifted between an overworld map and side-scrolling gameplay, Crystalis uses a 3-D overhead view throughout.
This is reinforced by the range of movement throughout the game's world. Where in Zelda the player always starts from the North Castle, in Crystalis one can save their location at any settlement--and with the purchase of a pair of inexpensive warp boots or the expenditure of a small amount of magic, instantly teleport to any one of them that they have previously visited, even if lost in the deepest dungeon. The ability to navigate the sea on a dolphin's back, and later, to overfly obstacles, also make the experience of navigating the game's version of post-apocalyptic Earth far more varied.
One should note, too, that the RPG elements are considerably more advanced. The game affords a more complex system for managing a larger inventory of weapons and other items (not just found, but purchased), and incorporates a number of charmingly innovative features, like the telepathic connection that the protagonist enjoys with the various teachers he encounters in his adventure. Non-player characters often display touches of humanity and humor (some of the villagers you rescue from Mt. Sabre proving real ingrates, and dealing with Kensu often a trial), while helping to make the storyline much more elaborate. And the miniature quests one undertakes are not just considerably more dramatic (mere water-fetching will not suffice to make a basement-lurking wizard teach you a spell), but more closely integrated with the larger adventure, which achieves something of an epic quality (most pronounced in the events at Shyron). Naturally the gameplay is far, far less repetitive than the conquest of Gannon's palaces.
All of this gives the game rather a deeply different feel--in many ways, a more attractive one, given our fuller immersion in a better-developed and more freely navigated world, and more fully fleshed-out story, superior to what any other 8-bit game offers us.
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