Here's a guess: You could be

plasma

I'm hotter than anything else in the world; I'm brighter than everything around me. I'll burn you if you get too close, But still, you know how to tame me.

Plasma is the hottest state of matter, and burns brightly (as in the sun or lightning), but we can control it for plasma TVs or neon signs.

Undesirable as I may be, I'm vital to preserving life. I'm not sure if you'll guess me right After all, I'm not who most think I must be.

The plasma on the sun sustains life on earth. However, when people think of the states of matter, they usually just consider solid, liquid and gas.

Here's a guess: You could be

plasma

I'm hotter than anything else in the world; 
I'm brighter than everything around me. 
I'll burn you if you get too close, 
But still, you know how to tame me.

Plasma is the hottest state of matter, and burns brightly (as in the sun or lightning), but we can control it for plasma TVs or neon signs.

Undesirable as I may be, 
I'm vital to preserving life.

The plasma on the sun sustains life on earth.

I'm not sure if you'll guess me right 
After all, I'm not who most think I must be.

When people think of the states of matter, they usually just consider solid, liquid and gas.