Wait for more Call of Duty: Modern Warfare Information
The biggest reason not to pre-order Call of Duty: Modern Warfare yet is that we don't know everything it. The new stream shared a lot of information about multiplayer and game modes, which is a good start.
We have yet to learn about how long the Call of Duty: Modern Warfare campaign is and what all it will entail. This is a key part of Modern Warfare, and if you are planning to play this mode, you should wait.
With Modern Warfare there is no Season Pass, so this will also be a new way for Call of Duty Points to play into the mix and for us to see how many new maps and free DLC options we get.
Don't pre-order Call of Duty: Modern Warfare with half of the info on hand. Wait and make Activision earn your money, especially if you plan to buy digitally.