RealMyst: Masterpiece Edition is beautiful, and I still love Myst, but I don't know if this is "the definitive version" of the game. Certainly it's the easiest to run on modern hardware, but I still would probably opt for Myst: Masterpiece Edition if only because it's better optimized and, well, costs a lot less.
If you want something that "just runs," though, or you're determined to freely wander Myst Island, this updated realMyst is your best bet. And hey, it's quite a sight to see the sun set.
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