Played it for the first time. Really nice.
Movement feels a bit floaty, but that's exactly how it was in Half-Life, so it's on point for the theme. Breezed through the tutorial, I liked how when I came to a switch, it told me to use F instead of waiting for me to fumble for the control scheme, which being a casul, I didn't memorize at first.
I ran around looking for a minute, looking for the mangeta key while I already picked it up. That's just me getting hypnozied by the fluid action and ambient music. I'm sure it wouldn't have happened again if there were more levels to be played. Not sure if it is intentional, but could only play the tutorial.