Have you ever read a book where you feel like you don't really care about the protagonist(s) by the time you finish (or don't) the story?
Have you ever written a character that makes you want to scream, "Who cares?"
There is a very basic principle in the art of characterization. In a very awkward, wordy way, you could say it like this:
It doesn't matter what your character cares about, if you don't care about your character.
Okay, so an interesting philosophy. But how do you apply it to your writing?
One possible approach is to look at the reactions of your character to the event in the story. If your story is rushing through the action of a scene, but we never see it from the emotional, physical and intellectual viewpoint of a unique POV character, than we don't have anything to connect with in the story. The natural reactions of the character are what allow us to connect.
So, every key or crucial moment in a scene needs an internal reaction from your character.
Not every moment:
(if the hero unlocks a door with a key, we don't need every intimate detail of that moment unless it is crucial),
...but the ones that move the story ahead:
(if the villain is on the other side of the door ready to pounce, we need to feel any pain or emotional horror resulting from being surprised or ambushed - not just have the actions of the event described).
It's just like that science law: action = reaction
When my kids scrape their knee or pinch their finger in a drawer, they don't come to me first with a tale of what happened - its always preceded with their reaction of hurt or pain. First the ouch, then the explanation. And as parents, we care about the emotion. We care that our child hurts, then we want to know why. If it were the other way around, we'd have to muster some sympathy for the drawer. Or the sidewalk.