We've done a couple of times and thoroughly enjoyed both times. We lucked out and had absolutlely perfect weather both cruises, clear skies and not too hot. Being down on the water makes it much cooler so even if it's a scorcher in town, it's much more pleasant once you get out there. I'm pretty sure the lower deck is air conditioned, we sat on the open air upper deck both times so I can't swear about the A/C. There's also a bar/snack bar available( I do remember the beer was very cold, I can swear to that ). It's well worth the cost, I would have no problem doing it again.
There is an entrance fee to get in the lake Mead national park, 25 bucks I think? You'll be amazed at how low the water level actually is, it's a completely different perspective traveling along the canyon walls.
Hope this helps.
