Along with waiting for information, the other major reason to wait is for Call of Duty: Modern Warfare reviews. This is a favorite series, but it is new and on a new engine.
It will be interesting to see how the campaign holds up to critics and other players once people can experience it in full. With darker subject matter, it may be amazing, or it could fall flat.
The other core features we need to wait for reviews on, or at least a beta, is to see how the multiplayer feels, what weapon balancing is like and what features are available on day one.
With cross play coming this year, it will be interesting to see how players match up and if this changes the dynamic with PC gamers finding more matches, but potentially at the cost of pitting controller wielding players against mouse and keyboard users. We need to see how this holds up in the real world.