There are a couple of noticeable differences in Half-Life: Source compared to the original game, however. The most noticeable is the water textures in the game which now have the same look and effects as they have in Half-Life 2. You can now see in the water when the large mutated fish comes after you. Also, character models now have ragdoll death effects when they die; no more falling through walls and doors when zombies and troopers fall by your weapons. Supposedly the entire Havok physics engine was imported for Half-Life: Source but unlike Half-Life 2 there are no real physics puzzles to solve in the original game. You also can't grab objects in Half-Life: Source like you can in Half-Life 2.