So I was going through The ten most addictive online flash games ever made posted earlier on /. Most of them I’ve played and agree are indeed addictive. There were a few that I haven’t heard of that were mildly fun, but then there was Portal: The Flash Version. I was just telling Xyon earlier today that one of the new games I wanted to play was Portal (which comes as part of The Orange Box) and showed him the trailer.
The flash version is a 2D version with basically the same idea. I got up to about level 30 before it was dinner time.