When you end up with a certain amount of PC games, it becomes frustrating to have them "all over the place." Sure, you can add them to Steam manually, but with that you lose a certain amount of Steam functionality and, if the game supports them, you can't earn achievements. It's not ideal, so when one of the best free-to-play multiplayer shooters on the market comes to Steam, you know you just have to download it again.
Blacklight Retribution is a great game, well deserving of your time and if you want a Call of Duty fix without the price tag, this is where you should be looking. Retribution is now available of Steam, alongside a brand new level, a Kill Confirmed game mode and a batch of achievements, weighing in at a little bit over 4GBs. It's a fairly stunning example of the Unreal Engine at work, offering enjoyable matches, a nice community and no entry fee.