I first tried to see the volcano last January after it re-opened. It was half the reason we chose to stay at the Mirage. It was already closed for repairs.
The 2nd time I tried was in August and it was actually open. It's phenomenal. You can actually feel the heat coming off the flames. The volcano is a combination of fire and water set to lights that makes the water look like fire, too.
My big complaint is that the show only lasts for about 5 minutes so it feels like it's just getting started when it's over. But it also starts every quarter hour, so that's a good thing too.