Yeah, it's a great spell, and I think it might come very useful in getting rid of a few Death Eaters.
However, Voldemort is a whole different story. Harry's gonna need much more powerful spells to get rid of Voldie baby! Dumbledore once said that it would take uncommon skill and power to defeat a wizard like Voldie even without his Horcruxes. Which takes us back to the ''power Voldemort knows nothing about...'' but that's a whole new topic...

Oh and I'm not sure Draco would've died if Snape wasn't around...but he would've stayed in hospital wing for much longer, that's for sure. And he'd probably be left with fair amount of scars.
Great spell all in all, I always knew Snape was a genius