The Spy
The spy is a class that can take on the appearance of any class and identification. He can also change his color and appear to be on the other team. The spy is generally used for infiltration and breaking down an enemy's defenses. He is equipped with a dagger, which is meant to kill opponents very quickly. If the spy ever scores a hit in the back the damage is quadrupled. Have a nasty sniper giving your team a hard time? Sneak up to him as a spy and knife him! The spy also has a tranquilizer gun, which shoot small darts that will slow down any enemy in half, including his firing and reloading rate. Unfortunately, if the spy attacks while he is disguised, he loses his cover instantly.
Spies can also carry gas grenades, which explode and release a noxious cloud of gas in a large radius surrounding the grenade. If you walk into the gas, you seriously start to freak out! You will hear sounds everywhere, see strange explosions and flashes all over the place, none of which are actually there.
What's new?
Not a lot has changed with the spy. The old commands still work - sfeign and feign function identically. The only difference is the death sounds made by players are longer and more drawn out. Disguising takes the same amount of time, and you can use binds or the menu system to do it.
The gas grenade range is altered slightly. The gas now goes higher, but not as wide. Not a huge difference, but noticeable.
One cool thing about spies is that the Half-Life engine makes the amount of blood that appears proportional to the amount of damage done. With the 4x dagger to the back, there is a LOT of blood after you knife someone. If you actually gib them with the knife ... well you can imagine.