HL serves up a veritable rainbow of colour with great looking aliens, electrical effects, open desert areas, office spaces, and big explosions. The graphics are sharp and easy to look at. There have been a few patches released in the last couple of years to bring HL up to speed with the latest 3D cards and advancements in network programming. The indoor and outdoor environments are excellent. Black Mesa is a big place and this is conveyed nicely.
Explosions are big and some of the scenery can be blown up.
The sound is also good. Playing with the headphones is probably the best way to play. The music is understated and subtle, playing only once in a while, but adding to the tension. Difficulty ramps up gradually, with Freeman facing more numerous and powerful aliens as the game progresses. The trip to the Xen, the alien stronghold, holds a few of the most challenging and terrifying enemies.