Possibly the greatest Half Life mod released, Counter-Strike is a hardcore FPS for the PC. Friends have been lost because of this game. It's clearly one of the most popular FPS games on the PC, and earned its spot as "Game of the Year."
Counter-Strike began years ago as BETA versions, up to 1.0 and now CS Source. Many mods have been created for the game to make the gameplay more intense, and if you aren't happy with your player or gun skins, you can easily find a website that provides more complex, detailed, or sweet looking skins to your game.
Gameplay - Two teams are formed when playing online, Terrorists and Counter-Terrorists -- each having various amounts of guns. Depending on the map, your objective may be one of the following: Bomb/Defuse, Hostage/Rescue, Guard/ Protect a Command Post, or Protect/Assassinate the VIP. There is an offline training course, which will teach you how to use each individual item. If you have 56k, I would not recommend it. The quicker your Internet connection is, the better chance of you blasting your opponents away without being harmed.
Graphics - Graphics are great considering the improvement over the years as newer versions came out for this game. Like I said earlier, if you aren't satisfied with your player or gun models, you can improve the qualities simply by downloading new ones. Some maps are quite simple, others complex. Although the default player models aren't up to date graphically, the gameplay is what really makes this game something special.
Learning Curve - This game may take some time to get used to. Good reflexes make for a better player, and tactics are needed when playing to succeed. I stopped playing for a few months, and when I got back into the game, it took about an hour or so to get my "skills" back and flowing. Practice definitely makes perfect -- or at least helps you improve in CS. Serious clans also look for dedicated players who can spend so many hours of a day to play CS. Tryouts are usually necessary to make a clan, and if you don't have what it takes, you are cut.
Replay Value - Believe me, this game becomes addicting! Whether you're playing with random people, on a LAN, or playing with friends, it's great fun. It's hard to stop playing. If you're a huge FPS fan like me, or a Half-Life fan, you'll have a hard time trying to quit
Sound - Sounds are recorded from actual weapons. These can also be adjusted and changed if you downloaded new sounds. Different mods on different servers may add several other sounds to the game, but the sound quality of the grenades, knife, pistols rifles, are very good.
One problem that has plagued CS over the years is cheating. Hackers are on the servers with the latest wall hacks, aim bots, you name it. It's these kinds of people that ruin such a great game, but Steam and VAC have worked hard over the years to try and reduce the amount of hackers, and progress has developed into a healthy online gaming environment. But beware! Hackers are still out there, and many gamers are not "noob" friendly. If you're bad, they'll let you know that, but as long as you're enjoying your experience, that's all that matters.
Counter-Strike deserves a big A+ for its L337|\|3$$