One of the key elements of a good climax is some sort of sacrifice.
The main character sacrifices something precious for the greater good. Whether she sacrifices her external goal, or her life, or something equally important, the climax should see her giving up something that matters to herself.
Sometimes it’s to do the right thing—she gives up her external goal or her life in order to do something infinitely more noble. Sometimes it’s because she has no choice—the villain is going to kill someone else or take away someone else’s livelihood if she doesn’t comply.
Sometimes it’s more emotional—the hero faces a deep-set fear in order to do something for someone else. Or perhaps the hero takes a risk in order to accomplish something for someone else.
Whatever you decide, your character should give up something extremely precious and important at that climax.
Why is this important? Because in sacrificing something, the hero has reached the Black Moment, where All Hope Is Gone. And in sacrificing something in order to reach that disastrous point, the hero has proved the reader that she deserves whatever happy ending—whatever miraculous turning of the tide—happens in the story after that Black Moment.
The reader will always want a hero who is worthy of their time spent reading. And what better way to prove worth than with personal sacrifice?
The hero acts in a noble manner that resonates psychologically with readers, thus ensuring pure satisfaction when the hero has a happy ending. If the hero hasn’t done something to prove her worth, then a happy ending for her will fizzle in a reader’s mind.