Easily my favourite module I've run in Season 5.
While I see some people state that "oh it's a dungeon crawl", the way the dungeon was laid out was well done. The puzzles that were on each floor forced the party to think and try a variety of options at their disposal. The other important characteristic I find in dungeon crawls is the "impending doom" component to it, and the encounter with the horned devils in the lava room was EPIC on that. And it wasn't even the final encounter. That encounter alone really forced my party into a pickle and I didn't pull punches with them (they are seasoned DnD players). And speaking of the final encounter, I loved the difficulty of it. Again, forced the party to use as many of their resources as possible and ended up dropping a few PC's.
My only 2 complaints about this module:
1) something needs to be done about Leomund's Tiny Hut. If there is going to be the stipulation about not being able to use extra dimensional travel in the tower, like Misty Step or Teleport, then something should be done to include Leomund's Tiny Hut and effects similar to it.
2) I play in a game shop and even with cutting out the 4th Floor, I still ran 4 hours for it. There's a lot available for PC's even without Abathor's floor.
Overall though, definitely memorable and had the PC's on their toes for the evening. Well done! 5/5