https://www.youtube.com/watch?v=ran_yU65Xmg
Honestly, i expected something a bit more involved than copy/pasting and scaling objects. And even then, this old ldjam game (Tale of Scale) does it better IMO:
http://ludumdare.com/compo/ludum-dare-25/?action=preview&uid...
(well, it doesn't do the copy part, just the scale part but still feels better)
Those non-euclidean rooms at the end of the video are sweet though. Honestly the most surprising thing is that we didn't actually see any of these in the portal games given that it's the same exact tech required to make it work as the portals themselves.
Edit: The concept looks boring, not the obviously unfinished tech demo
There is an obvious reason why F-STOP wasn't finished though: Valve never finishes anything. Episode 2 came out 13 years ago.
edit: and for completeness, nowadays I feel compelled to point out that the latest half life game came out just a month ago