While Clastle is not a terrible game by any means, it seems worse than it actually is because of how close it comes to being something special. It has an intriguing sense of atmosphere and an interesting (though sparse) story. However, there are a few major flaws with this otherwise sound run and jump platformer.
The main problem is the controls, which for pretty much any platformer spells death. The game controls fine with a game controller...except you cannot crouch. 90% of the time, this is fine, but it is necessary to switch to a keyboard when the odd puzzle arrives that requires you to duck. There are no setup options for controls to speak of, so you are pretty much stuck with the keyboard or semi-functional controller. Neither of which work on the menus, I might add.
The environments generally look very nice, and as I mentioned, they can be quite atmospheric. Sad that the main character has about three frames of animation. Even odder is that he carries two glowing knives in a game with no combat, and that instead of grabbing a hold of various poles and bars, he simply bounces off of them. That is, assuming you get the frustratingly nitpicky hit detection to register that you are actually touching said pole or bar.
While this may sound all doom and gloom, there's actually a fair bit of fun to be had here. While it's on sale for half price, I can still cautiously recommend this title. For the $5 standard price - even as cheap as it is - I would have to recommend a pass.