Contrast is a good game for people who are just starting out in the puzzle genre, but the more experienced puzzlers will not face any big challenges when playing this game.
The shadow mechanic is interesting and the puzzles are interesting, but there aren't very many and they aren't hard either. I was expecting something more and a lot harder. The larger puzzles still only take a few minutes to solve. If you're looking for a real puzzle game, you will be dissapointed.
However, the atmosphere of the game is great: the puzzles tie in nicely with the story, the collectibles (documents and photos) are actually worth collecting, as they add some background to the story and the story is quite funny at times.
If you're looking for a challenge, this game probably isn't for you. If you're looking for a nice story with a bit of player interaction, you'll most likely enjoy this. However, I'd suggest you wait 'til the game is on sale, as you'll easily play through it in under 4 hours.
In short: you like storie? Get this when it's on sale, it's very enjoyable but too short! You like puzzles? Better look for a more dedicated puzzle game.