I stumbled upon my brother's old Steam account one day and impulsively decided to install Counter Strike: Source, and I am glad I did.
Graphics - Great graphics once you have your video settings and resolution at a high level. The gun models and environments are rigorously detailed. The characters models are quite good as well.
Sound - There is no music, but the actually sounds in the game are great. The AI voices are fairly well done and the gun sounds are great. Hearing the same old AI voices can get a little boring though. Sometimes a little music wouldn't hurt, but an intense first person shooter sound isn't needed.
Gameplay - Stunning. The controls aren't complicated and are fully customizable. You are broken up into two squads: Terrorists and Counter-Terrorists. The terrorists plant the bomb or prevent the counter-terrorists from retrieving hostages. The counter-terrorists diffuse the bomb or rescue the hostages. From my experience half the time most people just try to kill each other and neglect the actual objective. The maps are widely diverse, and most are fun to play, preferably the map de_dust2. There are also user created mods that greatly change the graphics, sound, and/or gameplay.
Learning curve - Ridiculously steep. If you start the game now you will be playing against people who may have been playing for many years, from the original Counter-Strike game. There is no single player mode, but you can play against bots. However, bots do not you help you get better. The only way to improve your skills in this game is to play against human opponents.
Replay value - This game is highly addictive and never seems to get boring. There are still people playing this game from 5+ years ago!
Overall - A great game that seems to have a lot going for it. The only problem you might have is that it can get frustrating when you always get killed and never seem to get better. That changes with experience, just like in any other game. You can purchase this game in stores or download it from www.steam.com 9/10