Lafazar: It's debatable whether it's "better" and really a matter of taste. Personally I think the two games are actually very different concerning mood and atmosphere, so I like to play them both for different reasons.
Advantages Myst Masterpiece:
-better lighting and curved surfaces (it was just not possible in real time at the time realMYST was released)
-simpler and more intuitive controls, navigation is a lot quicker
-low hardware requirements
Advantages realMYST:
-free movement (makes exploration much less confusing sometimes)
-much higher image resolutions and even antialising possible
-changing weather & more animations (water etc.)
-additional age to explore Ugh, you did have to add that last one, didn't you? :) I was figuring that I might be OK with my old version, now I'll have to wishlist this one!