This game man, I had a lot of fun with it. If you want to play a metroidy style game that has tons of puzzles and riddles and such to solve? This game is something you should seriously pick up.
If you don't want to take notes/screenshots/etc though? You should probably look for another game. For the most part, all of the puzzles are pretty fair, but there are a few that kinda made me go "...really?"
If you're looking for a good challenge, I can not recommend this game enough. My only regret is that I didn't hear about it soon enough to get in on the kickstarter for the sequel they're working on.
That said, I admit to getting frustrated at the very end and succumbed to having a friend give me a few tips xD After 90 hours I was just ready to be done, ya know? It was kinda frustrating, but as a whole, I still love the hell outta this game <3