I have heard some badass v6's before. most of them were grand nationals LOL.
also, its not just the fact that its a v6 that will make it sound good or bad, you are hearing a lot when you hear an exhaust note.
short list of things that control your sound (besides the obvious exhaust parts):
cam
stroke/bore
exhaust port shape
tune
muffler placement (mainly referring to before or after axle)
muffler stagger (one muffler farther from the motor than the other)
weight/mass of material used for exhaust (notice how stock mufflers are a little heavy....)
this is why some v6's sound similar to v8's to the untrained ear, some v6's sound like they wanna be an indy car motor, and some v6's sound like you want to destroy that guys whole car.
there are a few 3.7 guys running around my town with full dog ass exhaust. yeah they make 300hp and all that.
For a little perspective I used to have a 88 T-bird with a 3.8. I wanted to go as fast as I could with zero money. because....well I had none. I made a dual exhaust for it out what I could find at the junk yard. I could not find a muffler that I thought would flow well AND fit under the car so I found 2 mufflers of the same type that would fit and cut them apart. removed some of the corrogated(right word?) pipes that looked restrictive and welded the mufflers back together. The result was surprising. The exhaust took on a tiny bit of drone at idol and driving speed, but it was just enough to make it sound cool and did not smash ear drums. at WOT several people thought I had a modded v8. Though I was not as fast as a modded v8 (back in the late 90's I would race a chevy 305 and win, also took down some newer camaro v6's at the time, but that was about it) the sound definantly made the car cooler to drive.