We did the walk in 2013 May (late review) and this is one of the most spectacular experiences I have had - You get to see the island expand right in front of your eyes and see how molten lava forms rock. We got to walk on rock that was just hardened, so you can feel the heat. You need to be reasonably fit to do this walk. But it's definitely worth it. We had to leave before it got dark since it started drizzling (and you are at a risk of acid rain, due to the sulphur) but if you can stay till dark, you can see the glow when it gets dark.