The design is great. I'm still going through it as a player, but so far there are only two or three things that I'd say are flaws:
1) Crater Mines go on and on and on and on and on and on
2) The second town (forget the name) is where you spend most of your time, but Homlet has all the detail.
3) It is very hard and approaches, but in my opinion does not cross, the line of fustration.
#3 is a matter of taste. #2 is quite pardonable given the history behind the making of the module. #1 is something we all learned because of RttToEE.
I don't know if you've read the module or not, but my DM swears by it.
All of the above being said ... it would be really swell if our party's fighters quit rolling 1s and 2s on their fortitutde saves. That can stop any time now.