While it is comparable to Portal, I think that it's a disservice to compare it as so. While portal is the manipulation of space, this manipulates time, specifically the time of specific objects as small as a pen to as large as the Earth.

The puzzles are wonderfully difficult, if admittedly a bit convoluted. Sometimes forgetting a single step means resetting the whole set-up for your solution. But this is all aided with how easy to use and smooth the entropy device is, even if the physics of objects don't play along.

Characters are average with Aria being particularly bland, but ARIA our plucky AI is light-hearted and entertaining, but mostly it plays a back seat to the overall "mystery" and story to the game.

TLDR: Worth the cost