The adventure itself can be really tough for the listed party levels.
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SPOILER WARNING
The really nasty encounters are the Grell -- which can take the -20 to grapple checks and still win every one of them -- and the mimic. Why anyone would put a mimic (which are very tough even at even CR) in an adventure where it can absolutely dismantle low-level PCs is beyond me.
Also, if the party fights the Animated Chain, BEWARE. It is incredibly powerful against the low-level (mine were 3 at that point) PCs.
Minor story issues: Think about the Last Laugh. That's one plot point my players instantly glommed onto. Patch is listed as an informer, but there is absolutely no reason in the module for the PCs to suspect him. The secret doors are very hard to find for 1st level PCs. The Vanishing is pretty brutal if the PCs are made with point-buy and have CHA for a dump stat. (I was lucky... the Sorcerer was the only one to catch it so far -- and coincedentally, the only one with a CHA above base.) Finally, the gear doors are BRUTAL until the PCs realize they need keys or to avoid the gears and find a way around them. Finally, the search DCs to find the gems in the middle of the Pulverizers (and other goodies in there in some cases) are very high -- 24. That requires a maxed search check and a very, VERY good roll for such low-level PCs.
Funny Story: My PCs killed the hobgoblins and made their way down the elevator. Then they went to camp at the bottom of the shaft. They were found by the hobgoblins that were going to relieve the ones guarding the top of the shaft. So the party flees back up the shaft just ahead of the hobgoblin reinforcements. I decide -- on the fly -- to have a hob jam the elevator by sticking his sword into the chains. The elevator slams to a halt, nearly dumping the PCs... especially the one in plate, who is saved only by the rogue grabbing him.
Then the hobs grab the half-dwarf and he sends the Animated Chain up after them (it has a listed climb speed, so it made sense to me.) The battle between the PCs and the Animated Chain on a tilted platform half-way up an enormous elevator shaft is probably the best fight I have *EVER* come up with. It was a blast.
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Despite having a few questionable monsters -- IMO -- this is a GREAT adventure. I highly recommend it.