From what I've heard it's sounds pretty noobish, I was on a vacation during the beta so I don't know much about, but what makes it so bad?

It's not really bad in my opinion. The reason people hated it so much is because it didn't really require any skill. But it is very easy to avoid. People were just trying to be reckless running around the map without a tactic. Pretty much if you do that you'll always get destroyed.
The only cheap and retarded thing I found and hated about the gun is that it had the downing ability. Which I think it should be an all or nothing weapon.

The Retro was more of a problem then the Sawed off. The Retro Lancer could down you faster then you could get 2 shots off with the Gnasher. Pretty much if you missed when someone had the Retro out you my as well just stand there and give up, because they just hip fire like a noob and your done in like 3 burst from that thing.

Every thing else is pretty balanced though. Although if someone had a controller mod the Hammerburst is pretty damn cheap to.

it wasn't bad it insta killed my opponents which was pretty cool although I like the gnasher more for the faster firing

Yeah, Sawed off has an 6-9 second reload time, while the Gnasher can shoot 8 bullets and reload in 2-4 seconds.

It's not bad, alot hate it and alot love it. Personally I don't like using it and it can get annoying being against a whole team using it but it's not so bad you quickly figure ways around it. It's only affective if the enemy is up close to you like a couple of feet beyond that it's useless.

yup it has it's downsides I hate the long arsed loading time

Yeah now they changed it so it has a light and a 90 degree angel, which if you think about it, that's the same range as the Gnasher. So it really has no advantage over the Gnasher. Other then it can kill 5 people at once.

100% reliable unlike Gnasher.

nah I felt as if the gnasher was reliable you just have to use it right