also the weight would come into play, there would be no need for extra ammo, maybe a few spare batteries other than that the lightness of such a weapon could have a large impact as there would be little to no recoil.= TOTAL DESTRUCTION.

Don't listen to the Movies; we will not use laser guns. There are a huge number of reasons:
1. lasers will make a neat hole through their target, but any hit Thats not on the heart, spine or brain would be useless.
2. lasers are dangerous, they will go through buildings having a high risk of friendly fire.
3. Armour penetration is not a factor, we could just as easily produce reflective heat absorbing meshes as opposed to normal ballistics armour.
4. Why make a totally new weapon when you can upgrade existing weapons to do just as good a job without needing expensive high tech?

If you want future weapons, then you should look into smart bullets that explode upon penetrating the target, that can avoid corners, and that can be made incredibly small. plasma/laser guns are a dud, forget it.