I replayed Portal 1 after over 10 years and finished it in roughly 2,5 hours (+- 10 minutes, didn't check the time precisely). I don't remember it as THAT short!
(Edited)

I replayed Portal 1 after over 10 years and finished it in roughly 2,5 hours (+- 10 minutes, didn't check the time precisely). I don't remember it as THAT short!
Yeah, if you think about it, the game can be cleanly broken up into 21 segments.
Each test chamber, the escape sequence, and the boss fight.
It's a great game for speedrun material, and the shortness makes it more replayable to hone your Portal skills. At least for me.
It's way, waaay shorter if you try and speedrun it. afaik you can beat it in under 10 minutes