Much has also changed with the player models that we are so used to in first person shooters. They are no longer just meshes of triangles with moving vertices. Within each model there is now a set of 'bones'. Valve calls this their skeletal animation system. When the bones move, it modifies the mesh around it. So your saying, so what? Well, it allows many, many more frames of animation to be added at little system cost (they won't bog down your system). This is possible because most other first person shooters set a certain amount of frames for each animation. In Half-Life, there is no limit to the amount of frames per animation. The only limiting factor is what your system can do :) With the new animation system monsters can be a lot more complex as well. Animations can also be much more complex than in other games. Valve can make multiple animations for each part of a model. So one animation could be a monster choking a scientist, and another could be it turning its head. Then they could put those together in the game so it turns and chokes at once. But if there was a third animation, one of it punching something with it's other hand, all three could be added together, or any combination of the three. Sound, one of the greatest cues that you're in danger. Half-Life takes sound to the next level with real-time DSP technology. DSP technology basically makes the same sound sound different in different environments. So the sound of a gun outside is different than inside. The sound in a small room is different than in a big one. The sound is also done in 3D. This allows the player to hear the enemies sneaking up behind him. 3D sound just kicks ass and should be in every game. I can see why it was so important to use 3D sound in Half-Life. The player needs to know where sounds come from in order to react accordingly. From the crowbar to spray paint... As in any first person shooter (FPS), a good arsenal of weapons is necessary. In most FPS games, you get the normal melee weapon, pistol, machine gun, shotgun, rocket launcher, and an all-powerful super weapon. Many of those weapons seem to be necessary in order to maintain balance and realism. Weapons like the Melee weapon, which is a bad-ass crowbar, pistol, machine gun, and rocket launcher have remained in. There are subtle changes to these weapons though. Now weapons are much more realistic than before. Could you ever possibly run while shooting some huge machine gun? You can, but not to the degree of accuracy that all the current FPS games allow. In Half-Life, standing still and shooting will cause the gun to jump all around and make it so you have lots of trouble hitting things. Forget about running with it; you would have a better chance of finding something good on daytime TV. If you kneel on the ground and shoot, the gun is nice and steady for some real killing. What they have added though, are some very unique, powerful, and some not so powerful weapons, all of which were added for one reason: to increase the fun of playing. One weapon added is the crossbow. In deathmatch, your name is on the quiver of the arrow. That way, all your enemies will see who killed them. Another weapon is the Tranquilizer gun. It lets you temporarily put your enemies asleep and you can steal their stuff. It must be pretty damn funny to tranquilize someone, and just stand there looking at him. Right when he can move again kill him to annoy the hell out of him :) The rocket launcher is a weapon that is standard in all FPS games. The difference with Half-Life's though, is that it is laser guided. No, it wont follow your enemy through a maze, but it will move depending on where you point the laser mounted on the end of the gun. There is even a can of spray paint. All you artists out there can cover the walls or enemies in your clan insignias, nicknames, or X-rated artwork... as I know many people will do :) There are even rumors surfacing about a Flame Thrower.