Pros: Community, Popularity, Compatibility, Fun, Mods, Price
Cons: Graphics
The bottom line: I recommend this game, because it's cheap and it's loads of fun.
Counter-Strike: Source is one of the best games I've ever played. It is known to be the most popular online game in the world, as every time I am on, there are always many servers with people playing on them. This game is compatible with Vista, even Windows 98. Almost any PC can run the game, as it is very lightweight on the hardware, but brings hours of fun. Plus, it is only about $20USD most places, so it's one of the cheapest games out there. There is over 100 maps, both standard and custom. Another thing that brings a whole other dimension to Source is Mods. With Source SDK, players can add a new complete customization to the game. If you get bored of the normal point and shoot FPS, then you can hop in a new server that has a different Mod installed, which changes the entire game. Surf mods allow you to cruise around at high speeds, Zombie mods allow you to play a hide-and-seek or runaway style game, while Gun Game or Deathmatch mods are just new, cooler versions of the standard Source. These game modes are sometimes more popular than the actual Source game. Counter-Strike is made by the same people who brought us the Half-Life series, and if you liked those games you will love Source.