We are Big Bus Tour junkies having taken them in NY and DC.
We were just in Vegas from July 28-31 during some brutally hot days. We knew they didn't have any air conditioning and were able to survive with a cooling wet towel and an unbelievable water thermos purchased at Costco.
What I didn't like is some of the women asked if they had water and they said the water is only for the tour guides. The bus company should provide water when it's 110-120 degrees.
There are basically two lines one for the strip and one for downtown. If you stay on the strip you need to hop on the bus and switch at Circus Circus. The problem is if you just want to go to say the mob museum you have to sit thru the whole tour and it could take you an hour and a half to get there vs 20 minutes in an air conditioned cab.
The wait to hop on ranged from immediate to 30 minutes.
The tour guides ranged from awful to excellent. Some of the guides are real characters and not in a good way but they do take you to all the major hotels and tourist spots like the mob museum and Pawn Shop and provide you with interesting stories about Vegas the hotels, history and people that built and live here.