OK, here are the bands I feel are under-rated, and why I feel that way:
Stabbing Westward: some of the best songwriting I've heard, period--particularly their lyrics. They were a minor sensation with their sophomore album Wither, Blister, Burn and Peel but even though their style of music was hot at the time they weren't promoted much. Unlike many bands, their music got stronger as their discography lengthened. Their final album was more commercially-oriented at the recording company's request, and while they managed to stay strong they received virtually no support for the album and disbanded. Though some could call it "selling out" I felt the fourth and final album was very strong and was surprised it wasn't more successful. They did what they were asked and did it well, and the company let it die.
Anthrax with John Bush: I always liked Anthrax, but like many felt as if they'd blown the formula when they fired Joey Belladonna. Well, after a spell I realized that Belladonna's subsequent self-named project was a joke, and listened to some Bush-vocal Anthrax. I was impressed. [Sound of White Noise], Stomp 442, and Volume 8 - The Threat is Real are to me, their strongest albums. Anthrax purists would disagree. I don't credit John Bush with the changes but I feel his contribution was strong.
The Scream: Had their debut album been released a couple of years earlier, they might have been a household name. Well-written and -performed "blues rock" with a talented lead singer in John Corabi. I've never even heard their second album so I can't speak on that one (Corabl had left to sing for Motley Crue), but the first album was a good listen front-to-rear. Unfortunately, it coincided with the advent of Nirvana's nationwide explosion and therefore was lost in the record companies' rush to publish anything grunge.
For the record, I detest grunge. Anything that would pass for a guitar solo during the grunge era could be played by a trained 6-month old chimpanzee. I like guitar solos.
Motley Crue with John Corabi: darker, more technical, and heavier than anything since Shout at the Devi, which was pretty heavy in '83. Who gives a fuck that Vince Neil wasn't there? I didn't care for much of anything they did after Shout at the Devil but was still a Neil purist; then I gave their self-titled album a solid listen and realized what they could be. No, it doesn't have the signature sound of Motley Crue... but yes, Virgina, it's probably their strongest work.
Type O Negative: they did it to themselves, really... or should I say Peter Steele did it to them. Sometimes they were silly, often they were way too depressing but when Steele's musical genius kicked in they were a great listen. Sometimes you have to dig to find it and obviously goth/death metal is not for everyone--myself included much of the time--but if for no other reason than to appreciate the nearly-orchestral arrangements, songs like Love You to Death, Black No. 1, Christian Woman, and Creepy Green Light. Lest you think Peter Steele a guy who had no vocal range of which to speak, I think you'd be impressed should you find a copy of Go to Sleep, a duet he did with Kat Bjelland for Songs of the Witchblade. It's not easy to find but it's worth it. I just discovered Peter Steele died a couple weeks ago. I will miss his music and his wit.
Junkyard: they had a minor hit with their song Hollywood, which was a decent song but not really indicative of their sound, which was what I guess you'd call blues-rock or sleaze rock. Their debut effort was a little weak, with the exception of a few songs including Simple Man, which I expected to be a cover of Lynyrd Skynyrd's seminal hit but turned out (in my eyes) to be a much-better song. Their next album, Sixes, Sevens, and Nines was much better overall but suffered the same fate as anything non-grunge released in 1991.
Rhino Bucket: call 'em an AC/DC rip-off band if you must. I admit there's a lot of similarity, but don't forget that AC/DC is a Rose Tattoo rip-off band, either. I think Rhino Bucket is underrated for that reason alone, which is sad because they seem to have more range overall than AC/DC. Georg Dolivo never sounds like singing is painful, as is the case with Brian Johnson since about 1987. As AC/DC is to Rose Tattoo, Rhino Bucket is to AC/DC: the imitator is better than the inspriation. I will admit, though, that I've not heard anything of theirs since 1994's Pain... so I can't say if they've gone up- or downhill, but they are still together to my knowledge.
That's what I've got for now. Others may come to mind.
)...so what bands/musicians...etc... do you think didn't get the praise/recognition they deserved? 
