I can't post too much, because some of my players have been known to read my blog, and I intend to run them through this module. So, just a few initial reactions:
-I like the inclusion of the "author's commentary" in the form of the Cheat Sheet; what would otherwise be an insane funhouse dungeon actually has a great deal of internal consistency. This changes the way I think about funhouse dungeons.
-Like Death Frost Doom, the dungeon itself has character. The Grinding Gear will most certainly not feel like just another dungeon crawl.
-Adventuring, and dungeon crawling in particular, is dangerous, and Jim Raggi brings that to the forefront of the module. People who muck around in places like this can get killed, or suffer unpleasant long term effects.
-The party can fail/lose, and doing so does not necessarily mean a TPK. I have read many a published module where the only two outcomes that are contemplated are the players killing the big bad guy/winning or they all perish.
I look forward to putting people through this module. I would say it is probably one of the most difficult modules I've read in a long time. A word of caution: you will not like this module if you are the type who prefers to solve problems with Knowledge skills or other skill rolls. The puzzles and hazards are all you, baby, and ain't no Dungeoneering die roll goin' to save you.
I shall post a play report once I've run a group through this.