Team fortress classic is....is....it's just awesome.
Team fortress originally started out as a mod for the quake 1 engine. It pretty much featured all the things that tfc includes but only done until perfection ( Until TF2 came along :P )
Most "Team" games would often in involve numerous players attempting to plow their way through the enemy base until one player reaches the objective. Team fortress classic puts pressure on the player for offensive and defensive positions.
Scout - Is the fastest in all the classes, used for clearing out light enemy's and discovering spys. Keep in mind that it can't take too much punishment.
Sniper - Armed with a high powered sniper rifle. Again he can't take much punishment. So don't be clever and storm into the enemy fortress.
Soldier - Armed with superior armor than snipers and scouts and wields a rocket launcher. But is one of the slower classes
Demoman - The Demoman can use his grenade launcher to fire into tricking spots or flushing out the enemy.
Medic - Very useful when healing other players in the middle of a battle.
Heavy - The Heavy is the most powerful class in tfc and wields a minigun. Although he is the slowest class and is a huge disadvantage.
Pyro - Almost every weapon he uses ( flamethrower, rocket launcher, grenades ) has some sort of method of setting the opposing team on fire. Once you or the enemy is on fire, waiting for the fire to calm is not recommend since you will find that 3/4 of your health is missing. Once set a light, better find some water fast.
Spy - The most tactical class in tfc. Disguising yourself has the opposing team or faking your own death to back stab the enemy for a one hit kill is very satisfying.
Engineer - The Engineer can build teleporters, ammunition dispensers and sentry guns to defend certain points of the map. But sentry guns require the Engineer to be constantly repairing them since they're always taking damage.
You can get it off steam for around $5. The only catch that there is lots of bot servers around, but people still play it.