Now that made me do a double take.
It's a fcking landing page, and they maked it so* wrong
Even in native you're likely to trigger Windows' "sticky keys" feature by pressing shift repeatedly (a standard keybind in many games). Back in the day, games used to crash on alt-tabbing so sticky keys killed your game until disabled.
The site itself seems to currently down but I was using just a few weeks ago. I found that port pretty impressive because multiplayer also works and still had lots of active players! (though ctrl-w for crouch and move forward doesn't, so I can't say it was a seamless experience)
Sadly main reason i was reminded of it is because the Doom 3 one seems to have better responsiveness for mouselook - the HL version feels a bit too laggy.
(though even the D3 version has a tiny amount of lag which i do not remember when i tried it a couple of years ago - perhaps changes in the browser are to blame)
I'm not even using a QWERTY layout, so I have to contort to press W... It's a common issue with US-made games.
New game > Select level > freezes here.
Making the full game playable would probably be less OK.