I've never really been a shotgun fan, to be honest. I rarely use them in any game.
But I found myself with the Alien Rifle, SMG, and Pistols, so I was hoping there would be a shotgun to use somewhere.
The Sniper Rifle is great because it lets me approach fights differently. Especially the Flashpoints. I run up to a building above them and can eliminate the entire group with no trouble in moments.
I've played around with Dual Pistols and the Rifle some, and both are decent, especially if you can get headshots. But I really need to start upgrading to get some real use out of them, I think.
I think the Sprint Beatdown is a bit overpowered though. I mean, you're invincible during it (kind of necessary, since it steals control from you), it instantly kills almost everything, and you can absorb any drops from enemies before your invincibility even ends. It's also extremely easy to target. I dunno, it just feels a bit imbalanced.