Counter strike was once the most popular online game in the world, now it is rising again due to a surge of people buying it in recent months. It is not COD, for those who have played half life 2 it used the same source engine just updated.
There are options on the game like deathmatch, that appeal to the COD kiddies, but it's competitive modes are only 5 vs 5 games where tactics must be used to win. It keeps kiddies away via a punishment system, for example if you quit a competitive match before its finished you will have a 'cool down' period which can last 2 hours. During this time you cannot play the game.
Al is correct there are no vehicles, but its a counter terrorism game, where you play as CT (counter terrorists) or T (terrorists). There are too types of maps Defuse, where T's must try and plant a bomb on a target and CT's must try and stop them planting or failing that defuse the bomb before it blows. The other maps are hostage rescue where CT's must enter a building/ complex and get the hostages ( which you must carry on you back) to a rescue zone, whilst the T's try and defend them.
Map sizes are pretty decent for a game with no vehicles, and they are multi layered with lots of routes to the objectives sure as; ventilation shafts, sewers, tunnels etc... means the defending team has alot of palces to watch. Note: They are bigger and better than cod maps.