This scenario was interesting, challenging, and exciting.
Massive demon invasion? It definitely was that, and it felt like a credible major plot point tying in with so many of the non-Lissala plot scenarios in Season 4. I can't wait to see what the bad guys are going to do next.
The interaction between tables was smooth and fun. Our GM informed us that the color of each zone on the big map indicated different buffs and debuffs for the encounters we faced. Also, as a Seeker table (12-13), we were able to give aid to our nearby tables each time we finished an encounter. One of them actually cheered when I told them that the King of the Gnomes sends his aid.
We had no cleric, but we did have a paladin. We knew going in that our objective was to win the Race to Zero. With two barbarians hitting VERY hard, a conjuration wizard, and a very skilled sorcerer, the lack of true combat effectiveness from my rogue/Pathfinder delver was mitigated quite a bit when faced with enemies immune to precision damage. At least a couple fights required Breath of Life and similar types of magic. To me that says the encounters were well-done and presented a good challenge without being overwhelming. (Although we did not get the opportunity to fight our final "boss" because time expired.)
There are only two things keeping me from giving the scenario a full five stars. One is that because many (or all) of the encounters during Act 2 are random, we only faced one role-play encounter. We would have preferred more role-play scenarios, and I can't imagine tables facing all role-play or all-combat when that's not what they wanted to do. As I also mentioned, we ran out of time and were unable to fight the monster in the final encounter of the scenario. We might have been TPK'd by it, but it would have been a tale to tell - and that's what I enjoy most, having a tale to tell.