Being composed of something that is "awesome (awesomesauce), true(trufax), in need of more (desu and cowbell)" it is mainly used to describe something good that you want more of.
Wow! That ice cream was awesomesaucetrufaxdesucowbell!
adj: Take awesome, multiply it by the power of awesomesauce, then multiply it by the sheer awesome of a thousand ninjas, and you will have something that is pretty close to being awesomesaucetastic.
"Dude, did you see that guy? He just somersaulted off a 20 story building, fell 170 feet, snagged a kitten out of a tree, landed on his feet, stopped that guy from stealing candy from a baby, discovered the cure for cancer, and established world peace!"