Dialogue is the workhorse of your story.  It holds tremendous power, ageless beauty, and amazing versatility.  I dare you to name another device that so effectively drives the story forward, conveys emotions, defines intent, triggers action, masks a lie or spills the truth, reveals character or lack thereof, and elicits reactions ranging from laughter to tears.  Dialogue pulls us in, wines and dines us, and then beds us down for the night.   

...BUT...

Dialogue has to be REAL (i.e. true to the character).  Readers pick up on things like that.  For example, if your character is a boring dolt he won't be the life of the party, impressing the guests with his compelling wit.  The heroine of the story won't lull us to sleep.  The evil doctor turned psycho lizard won't be telling jokes...or talking at all...come to think of it.    

In the discussion of  "showing vs. telling" (the age old writer's adage), dialogue is a much more effective (and interesting) way to "show" the reader what you want to convey.  Don't tell me the new soccer coach is a hot head.  Show me with his angry outbursts at the players and parents.  In other words, show me with his words, don't tell me with yours.    

Dialogue is also a great fixer.  The next time you hit a flat spot in your writing—inject dialogue.  Spark up a conversation.  Start an argument.  Whatever.  Just crank up the dialogue and then hold on tight.  That horse likes to run.