They have hooked onto an absolutely brilliant way of porting old puzzle games into the Source engine - and added a great half-lifey story - but they didn't appear to be taking advantage of it by making it a full-game. It felt more like a long demo version of something that needed more. Although I admit they might eventually suffer the same problems all puzzle games get with excessive length - repetativeness.

That said, I wouldn't have minded a little bit of repetative play just to experience some of the cooler moments more than once without having to play it again. There was some great flinging you could do in that game and I honestly just stopped ten minutes in and was pissing about for well over two hours :P There's so much you can do with portals, especially if you time opening new ones right. Have you done the 'super cube cannon' trick yet? Get one going between a portal on the floor and ceiling, then open up a link to your floor portal somewhere else and watch the cube shoot out like a bullet :D

Yhorian