Yes, yes, I know, plot is important too. But think about it, why are the popular books popular? Because the readers identify with the hero. Is the hero a vampire, hobbit, or alien? Could be. But that doesn't mean we can't identify.
No matter what world your story is set in, no matter what situation your character is in, it is the thoughts, feelings, and interactions with others that make the story worth investing time in. Take HP for example. Yes it would be awesome to discover we have wizard powers and can go to Hogwarts, but it's the relationships between Harry and the others that keep us reading. It's wanting to see this likable kid who's had a bad time of it come out on top.
Can we the readers identify with Harry? Of course! Are we wizards? Did we grow up in a broom cupboard under the stairs? Probably not, but we've sure been the odd man out at times. We know what it's like to be the underdog or feel inadequate or awkward, right?
When you write, you have to draw on those experiences and emotions you've experienced. Even if say, you're MC happens to be a leprechaun and is facing his worst fear - a wild unicorn, take that time you were five and the giant doberman next door got loose and ran right for you. Then just... extrapolate! That's why we're writers after all. ;D
What identifiable traits does your current MC have? Which MC have you fallen in love with and was it because you were ale to live vicariously and identify?