I just downloaded the demo, and i cant tell the difference between that and the original, the levels are even the same, does anyone know if there are any differences?

I believe it's the original Portal game with a whole bunch of extra levels and missions added.

Yeah it's just had a shitload of levels and missions added, im yet to try portal.

I found this to be a very good game; I hadn't tried portal and bought this instead.

The ending credits are neat as well.