There are a few ways to determine if your characters are good enough. I know, I'm not the best writer. Agreed. But as an avid bookworm I do know a good read.
If you are all done writing your book and are going to close the covers on it, ask yourself. Is there anything you will miss about the characters? Does he have an alpha male quirk you just love? There needs to be a yes, here people. If not, your character may not be good enough.
If your characters somehow switched their minds and bodies, would anyone notice? Do your characters all sound alike, act alike, or is there a definite set of personality traits for each person? Would someone say, hey that's what steve would say, or do you have the dreaded cardboard characters syndrome?
Do you love your book enough to write sequels about it, (even if you can't think of any right now, or have no plans to do so) or are you bored with it? If you're bored, it could be you have been plugging along on it for a while and need a break. That's okay, but if it's just plain boring, it's going to be a lot harder for a reader to care.
These are common sense questions yet ones I rarely remember to ask myself.
Another way to help a failing book is to ask yourself, what cou8ld I add just for fun? Never mind if you would never do such a thing, ask yourself anyway.
Would a dragon dropped in the middle help things along? A sudden invention of magic? Another character? And when I asked myself that, I went, oh! Perfect. oh oh. Means the main squeeze is not good enough. John, your failing in your role as alpha male, buddy.
If you think a sudden creature is an improvement to your novel, you need more action. If you wish characters could do magic, there not interesting enough. If you think a funny or heroic character is needed, someone has cardboard syndrome.