"I'll explain: Before you can launch Modern Warfare 3, you have to launch Modern Warfare 2 first. Seriously. "Call of Duty HQ" is just the Modern Warfare 2/Warzone client under a new name.
Switching between Modern Warfares 2 and 3 from the HQ is not like switching modes. Once you're on the main menu, you could jump immediately into Warzone or a multiplayer match of MW2. Clicking the Modern Warfare 3 button, however, closes the HQ app and launches an entirely different executable called Modern Warfare 3. There is no option to just launch Modern Warfare 3, because "Modern Warfare 3" is not its own game. It's buried, literally, inside CoD HQ as a piece of add-on content.
The result? It takes 70-90 seconds to launch Modern Warfare 3—at least, those are the times I'm getting. That's an eternity for CoD, but what's baffling is that these extra steps serve no discernable purpose for players. Perhaps Activision pitched the CoD HQ with consoles in mind, where games aren't so easily organized by series and an app that switches between the handful of still-active CoDs is useful."