OK, the graphics are absolutely stunning, but that they were already in Riven. The only real apparent technical progress (and not the least, mind you) is the 360 degree view, which lets you immerse into the breathtaking sceneries of six (or more acurately, five and a half) different ages.
The puzzles are in the same logical vein as usual, but sadly I didn't find them very challenging and I was able to finish the game in approximately 12 hours, which is much less than what I was expecting from the creators of the Myst series.
As a whole, Exile is a wonderful game, mysterious and beautiful, and the music sends you directly into another, totally magical dimension, but if you've already played its prequels, no doubt you'll be left begging for more. My guess is that people with less experience in the Myst universe will enjoy it much more. I can only recommend they play Myst and Riven (in this order) too.