Maybe not the best idea.
Call of Duty is undergoing a bit of a rebrand on Steam, with the Modern Warfare 2 Steam page being retitled “Call of Duty” and the game itself being split into an entirely new store page.
Why is Activision doing this? A cynical person might think it’s because Modern Warfare 2 has a 57% mixed rating on Steam and Activision wants to obfuscate negative reaction to future releases by stuffing their games under a single app. Good luck with that. For the record, Activision is claiming that the move is to make things more straightforward.
An explanation I don’t think anyone is really buying.
Going forward, future Call of Duty® titles can be played from the same location on Steam. This should make deploying to the battlefield even more straightforward, so you and your squad can worry less about where to launch and more about how to score your next victory.
Whatever the case, the move makes Modern Warfare 2 look like a dismally failed indie game right now. It’s been seven hours since Activision flighted the game to its own app, and 109 people have come back to review it. The problem is only 22% of those reviews are positive giving the game a “mostly negative” rating.

There’s a few cynical interpretations you can make out of this. Obscuring player counts, the possibility that Activision will sell future Call of Duty games as DLC in order to get around Valve’s refund system. Steam’s DLC policy allows for refunds of DLC within two hours of purchase unless the DLC has been “consumed.”
DLC purchased from the Steam store is refundable within fourteen days of purchase, and if the underlying title has been played for less than two hours since the DLC was purchased, so long as the DLC has not been consumed, modified or transferred. Please note that in some cases, Steam will be unable to give refunds for some third party DLC (for example, if the DLC irreversibly levels up a game character). These exceptions will be clearly marked as nonrefundable on the Store page prior to purchase.
Activision has not made a statement about releasing games as DLC, but if they’re going to have a base app then it does seem plausible.
Best of luck with the review scores though.