I couldn't classify the game as hard puzzle game because it really isn't hard. However, being hard isn't at all defining how awesome the game is. It's a 'box' puzzle game where you have a certain object before you - some sort of a box/contraption - that you have to unlock by learning about it and revealing its nature by exploring it, which in turn allows you to unlock parts of it and so on until you solve it. There's also a short story as background context if you're interested.

All in all this is a great game that rewards curiosity and imagination. The graphics (lighting, geometry) and sound (ambience and mechanical sounds) are superb and in a way satisfying. The only downside for some is that the game is short but, honestly, I personally enjoyed every bit of it and think that 'more of the same' would weaken the experience. There's a sequel, which hopefully will provide a twist or improve on the original.

If you like puzzles, this game is a delight, and I wholeheartedly recommend it.