It's definitely a must see spectacle while you're visiting Las Vegas. Gets a little too crowded, so get there early! The volcano erupts nightly at 7PM and 8PM, plus 9PM on Friday and Saturday, so you have only a few chances to see it.
The middle area is the best place to see it, you really feel the heat and the warmth from the volcano when the fireballs erupt. As a little trivia, I have heard that they removed the mercaptan odor from natural gas and added a pina colada incense.
The projection mapping was so so.