So, what's the deal with shotguns? They overheat after a few shots. Seems like a major limitation. I'm playing a vanguard on my second playthrough (trying to score some more specialist achievements), and I've basically left my shotgun skill undeveloped in favor of pistol.
The bonus skill was a tough choice. I have First Aid, Electronics, Decrytpion, Damping, and Sniper Rifles to choose from. I went with Electronics, because the shield boost it provides should be pretty nasty in combination with Barrier's protection.