Personally I'm not really running the module but using it as a resource for my current Underdark campaign. In terms of my usage it's great, as it has lots of good content to mine, but I wouldn't want to run it as is because I don't think the plot really works. I think the Demon Prince problem can feel too distant and radically beyond the power levels of the characters for them to really engage with, and the main motivation the module gives the characters is to get the hell out of the Underdark.
In my experience the plot is unnecessarily convoluted and doesn't really do a good job of providing motivations for the characters to think that they should stay in the Underdark and fight Demon Princes. I recommend either coming up with your own plot that actually makes sense for the player characters and gives them better incentive to stay in the Underdark, or else just run the opening chapters, have them escape the Underdark, run some unrelated adventures with those characters until they are higher level, and then when they feel qualified to save the world send them back to have some epic Demon Prince fights. The adventure is actually sort of set up for this (they are supposed to leave and then be summoned back after some time has passed by a Dwarven lord who needs their help or something like that) but if you aren't planning around doing that then you'll be put on the spot by them leaving the Underdark.