I ran this scenario for four players on tier 10-11. They managed to make it through without any significant trouble mostly because of balanced party composition. I have also played this on the lower tier with six players. We had a bit more trouble, but managed to squeeze through.
The scenario offers plenty of opportunities for many types of characters. There is a social encounter, two skill encounters and a couple of relatively challenging battles.
The map is unique, but easy to draw and comprehend. Also the fact that there is only one map makes this scenario easily playable with only a basic flipmat.
I also like the fact that things like the height of rooms and climb DCs have been told in the scenario. And what happens if the PCs decide to run and rest before facing the boss.
A slight minus for some editing mistakes, but the scenario writer has provided answers on these forums in the scenario thread, so check there if running.
Large is good word for describing this scenario. Everything seems to written with epic in mind. I'd recommend other GMs to try and give the players that sense of scale. Otherwise it might fall a bit flat.
I ran this scenario for the lower tier, full six players. They were somewhat challenged, not overly so, even though they did end up fighting in the end. In lower tier this does not hurt them as much as it might in the higher. Just they looks on the players faces when they realized what they're facing was priceless. The one time when metagaming actually works for the GM.
Minuses come from certain annoyances. The ally side bars are good to have, but by the time they're to be used most, they're all over the PDF, and thus require lot's of scrolling. And the Cheliax mission is a bit too complicated, and the actions of the other characters can make it impossible. It is also a bit unclear whether Zarta is trying to make all the characters participate in the more overt part of the mission and then give the Cheliaxians more to do, or are the other PCs just supposed to ignore her first message?
I would have liked to give 3,5 stars but that's not possible so 3 it is.