Pros:

New model, nice textures, very realistic looking laser sight attachment.

Cons:

Needs to be darker and more sharper with some more lightning and darkening on edges.
Should be normal M4A1 without removed carry hadnle and additional RIS, as National Guard doesn't use a weapon that looks straight from Navy SEALs in Afghanistan.

Conclusion:

Very good choice for L4D, it would be realistic to see this on dead soldiers and pick it up from them.