The climax is the most exciting point in your entire story; everything that you have been writing culminates at one point. So how do the characters that the reader has been following relate to this massive event? Why are they putting themselves in life threatening danger, and how does the climax affect them individually?
The climax needs to important to everyone involved. Think of your characters as normal people, even if they are incredible heroes. Would the average person bust through a police barricade to tackle a gunman with a child as a hostage? Probably not, but the father of that child might. If you make the climax personal, then the reader will feel the stakes get higher. Even if the climax is important to your main character, why does everyone else care? Everyone should do one of two things in these pivotal moments. Fight or flight. Make your climax chaos, and incorporate that chaos into your characters actions.
Climaxes are also turning points for character arcs. A good character does not enter and leave a climax as the same person. Take those traumatic events and make them real. If someone dies, make his or her friends mourn. If a lot of people die, show the damage, both physical and mental, through the survivors.
The climax should be epic. Make it stand out by making your character’s the most powerful that they can be, but don’t cut it short. Let the reader relish in their newfound powers. Give the reader something to cheer for. After you give your characters a good portion of success, destroy them. Do something that cripples your characters so much, that the reader’s stomach drops. That way when they barely squeak by, the reader can feel that all the effort they spent reading your novel will be worth it.