Counterstrike Global Offensive

Although CS:GO is a bit older it still is a great game and does offer plenty of the old fashioned CS fun. By now the map choices for this game have become quite extensive especially if you pay of the pay-pass giving access to community generated maps. Also it is the first CS that came with the Gun-game mod as part of the default game.
The Game itself offers the good old CS system tried and proven with a face-lift. There is nothing unbalanced about this CS version compared to all the prior once.
It is also one of the participating games in the Steam Trading Game Beta and that could also encourage some people to play since it adds an extra collecting incentive.
The game is of course powered by the source engine giving it plenty of eye candy appeal even for a slightly aged game.