I just finished playing TCD, and enjoyed all of it. I got a solid few hours of gameplay, but was still left wanting more. I hear there are multiple endings so perhaps I'll go back and find them. There's definitely some replay value there.
The game does a good job of describing its alternate reality, but manages to avoid lots of exposition, and the story is nicely fleshed out during gameplay. The map design is great, making me think hard about where I had to go while not requiring me to retrace my steps much. Often I felt tested, but without being frustrated.
The combat is well-balanced and there are a variety of enemies and weapons. The upgrade system augments the gameplay nicely, without dominating it, and the recycling system is super cool; I wish I got more out of it the first time.
Overall I'm really impressed. Sequel please! :)