Having played this scenario and talking to the GM afterwards, I can see the definitely see how the potential level of lethality could turn off many players.
My friends and I went into this eyes-open knowing (or at least assuming) that we were going toe-to-toe with one of most powerful wizards in history and his minions.
The party was very well balanced. In addition, we stocked up with expendables (scrolls, oils, etc) that really gave us an advantage in the various encounters.
The final encounter almost ended prematurely when my brawler "one punched" the big bad with his knockout after the GM rolled a "1". It was downhill (for him) from there.
Regardless, we had a great time. The table played like a team and our GM was great. Luck did play a factor -- we had some amazing rolls while the GM had some poor ones. It could just have easily swung the other way I supposed. But it didn't.