Actvision's producers talk about the new ways that weapons usage will change in Call of Duty: Modern Warfare 3. It sounds like the more you use a particular gun, the better it gets. Peep all of that and new weapons in the clip above.
See, now THIS looks fun. Some nice, action-packed multiplayer.
Also nice to see they've changed the weapon upgrade system from MW2. I didn't really like that you had to get kills with certain attachments on to get new ones, rather than just getting to choose your attachments. But that seems to have been fixed.