With higher nic levels, it definitely hits the throat harder and adds more peppery sorts of overtones to the flavor.
Bad nicotine, on the other hand, can have a distinctly funky flavor. I only use Wizard Labs or MFS for my nic and haven't had any issues, though.
Strangely, as my nic level has come down I've also been using more VG. I find I enjoy the smoother and very slightly sweet flavor as a note to my (mostly) menthol.