Differentiating rifle type weapons

[Galapogos]

After watching all the E3 footage we saw a lot of people playing the light and heavy assault classes, and a little of the medic and engy of I remember corretcly. This means we at least saw a lot of carbines and LMGs. The thing is I did not see a huge difference between the two in how they handled. I would like to see the rifle type weapons (SMGs, Carbines, full sized ARs, and LMGs) have significant differences in how they handle and also what situations each is the most effective in, or at least how they can be used to approach the same situation from a different angle. I didn't mention sniper rifles since they obviously already have a very defined role.

A very simple solution to me would be to restrict ARs to single/3 round burst and the rest to full auto/3 round burst, but I don't think that would differentiate them enough, even though I am sure there will be differences in rof, dps, etc. as well obviously.

How do you guys think these weapons should be varied so they have clear differences in performance and function?