Portal is one of my favourite games ever. I've completed it at least four times now on various platforms. It's full of humour, clever design, and is sufficiently short.

I was worried about the sequel bring expanded to a full game, with the ideas stretched too thin. To a slight extent this has happened - but mainly to the story, which is a little weak at times. The way the game is separated into sections works well to break up progress, and I've just finished the set of levels introducing the repulsion gel. The weakest part of the gameplay is in a few of the between-chamber sections which rely on you spotting a wall in the distance where you can throw a portal.

The story hints that I'm closing in on the end now, but I've heard great things about the co-operative mode ... I just need to find a companion!