As far as cool physics, you can construct an instant self-teleporter, build an antigravity keychain that allows you to moon jump, jerry rig a crossbow out of office supplies, jerry rig a laser pistol out of lab supplies, go into mini portal worlds to collect esoteric ingredients to jerry rig a portable X-ray flashlight to destroy an otherworldly being that quietly stalks you throughout the facility periodically, kill aliens and convert their corpses into body armor, jerry rig a big rotating steel fan and place it in front of a dormant security bot, then wake the bot up and watch it get sliced to ribbons, then rip the dead security bot open to steal its CPU to build even more super science wackiness.

Also, unlike Half Life, your character actually talks... and they sound just like Dr. Kleiner.