Pick up Black Mesa or see if there is a demo. It’s a fan-made remake made recently that might be easier on your eyes. Additionally, you can open up the developer console and enter:

sv_friction 6

This the movement friction from the default of 4 to 6 to make the game less slidey.

The motion in HL1 is quite odd as you somewhat slide around rather than walk. It was quite normal back in the old days of Quake but if you’ve played mostly modern shooters, I can totally get how odd (and potentially motion sickness inducing) it is.