Uru is a somewhat bittersweet experience. The fact of the matter is that it's a broken game; divorced both from the safety of conventional design and from the massively multiplayer online play that was to be its centerpiece, Uru exists today only as the ruins of a grand, unrealized vision. But what spectacular ruins! You don't so much "play" Uru as wander its massive halls, gaping at the fantastical colors and textures and shapes, and pondering what it must have looked like in its own time... what it might have looked like if history had been different. Uru is beauty tinged with sadness.
And what'll really bake your noodle is that this is all what Uru is literally about: wandering the ruins of the long-dead D'ni civilization, the "holy land" behind all the mythology of the Myst universe. I have been a Myst devotee since the beginning, and playing this game back in '03 was a parade of jaw-dropping discoveries: "This is neat, it could almost... oh, my, GOD - am I where I think I am???" From there the game develops a strange recursive energy: we're seeing things "for real" that we only imagined before, but they're still just bones and we must imagine further what they looked like long ago on our way to the game's putative (and unrealized) goal of bringing it all to life again. Adding on top of that the fact that the game itself has become a similar boneyard, an emotional resonance is achieved beyond, I think, even what the designers could have originally intended.
To be sure, I don't believe Uru's online side was ever going to or will ever succeed in this form. It was given a fair chance and failed on its own terms. While it's loaded with authenticity and emotional power, it never managed a satisfying storyline, or even totally coherent gameplay. Uru gets something wrong for everything it gets right, and, while I hope it is reborn in the future, it will need to rethink its core design ideas to be reborn successfully. That said, perhaps the best thing about Uru is its design creativity. People often say they'd prefer a game that tries new things and fails than a game that plays it safe, and this is that game. Even when Uru falls flat on its face (a couple puzzles have even risen above the original's maze puzzle in adventure game infamy), it always manages to fail in totally unique and interesting ways - ways that spark conversations about how game design works and what it might be capable of in the future.
In short, this is not a game for people who want a complete experience - like Riven. This is a game for people who just want to explore and to think, with no reward for it but the beauty that is all around.