Let me start by saying everyone's opinion is equally valid, because photography is an art form and we all see it differently.
So here's how I think about B&W.
I can't say what absolutely makes a good picture, but I can say what I don't like. And that is images that are just grey. To me a really strong B&W should have areas of pure black and pure white. They can be small, but I think the pure blacks give a much richer image, and the pure whites help it stop being dirty and dingy. I'd possibly concede that it could be one or the other if you were going for a high key/low key look.
To that end, if you are using LightRoom, there's a technique called the
'J' trick that shows you where your clipping is happening. It works for both B&W and colour, though I rarely use it when processing colour images. Essentially, you adjust your sliders until you just have some clipping (or go overboard and have loads) to ensure a full range of tones.
I recently went to the
Sebastião Salgado exhibition and to me that what a well-exposed/printed shot should look like. I mean, it helps that his subject matter is often important. I'd also argue that seeing an image blown up that big and hung in a gallery also adds to the aura of whether or not it's 'good'*.
I don't know much about he approaches his work, but one trick to try if you're looking to see a scene in B&W is to squint at it and see if you can differentiate the colours. Very often the only thing that separates them is the colour rather than the tone. If you can't see the differences, then they'll merge into one grey mass in a conversion - unless as has been previously mentioned that there's some form of texture or other way of creating/seeing contrast.
The best thing to do is look at B&W photography online and bookmark the ones you like and then work out yourself what it is you like about them. Is it purely subject matter? Is it the aesthetic of the image itself?
*Back to the Ansel Adams debate, there is an aura about him that smacks a little of emperor's new clothes. Not so much from him, but from other people. There was an experiment I read about recently where they got some Ansel Adams images that were less well known and asked people to judge them. I think within the same experiment they also had images that were attributed to him.
Essentially, once people knew it was his work, they rated it more highly than the images that were just presented as anonymous - despite being the same photographer.
Now, I'm not sure how robust this experiment was. I don't really remember it well enough to know if the anonymous images would be images that Adams himself was proud of. Or if it came from his back catalogue.