Somewhat related, but you can also play CS 1.6 in your browser: https://news.ycombinator.com/item?id=23497236

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)