if you wanna play this and actually have a fun experience, check out Half-Life: Source Fixed. This game appeals to me mainly because of the le funny ragdoll physics. if you really dont care about that (and I assume most wont) just play the og.

Absolute ♥♥♥♥♥♥♥. Only use is for gmod content

Bought this on sale for the funny bugs, but was just in time for Half-Life Lemmings to come out. Mostly worth it for the modding and Gmod, but there are community patches to make it... functional.
Also pushing boxes has never felt better. If only they did the expansions like Blue Source, or Opposing Source