Last time, I was rather testy at the first half of this adventure. I did finally power through reading the rest of it, and it was better. Of course, nothing's perfect, so I figured I might as well give my thoughts on improving the rest of the adventure, too.
The priests' quarters get off to a rough start by declaring that every entrance from the maze has a compass rose carved prominently into it. There's no reason I can imagine for doing this other than to facilitate using compass directions for boxed text, so it should be obvious that I'm going to dismiss that reasoning and ignore that detail. The random encounters are mostly sensible for a change (the dervishes coming in far smaller numbers than elsewhere is a nice touch), but I'd move the wizard from the maze up to here and note that NPC, the knight, the cleric, and the thieves as all being one-time encounters to represent the scattered remnants of the paladin's party. I'd get rid of the giant spider encounter as well, probably replacing it with some ambulatory ooze, as that tends to fit well with undead.
For the keyed encounters, the fruityflies and exploding pineapples seem excessively silly. Sometimes a magical buried oasis can be just a magical buried oasis. Given that they're grown from the waters of Athis, I'd be fine with the fruits of the oasis retaining the same steroid properties as the fruityflies. The encounters of "2 figures are huddled in the middle of the corridor, and they attack!" are lame, so I'd just remove them and rely on random encounters to fill in the gap. The treasures from those areas can be stowed away in random sarcophagi, giving more incentive for the players to search all of the sarcophagi they come across and thus trigger the encounter in the "catacombs" (which aren't really catacombs, but I digress). The worthless statues should at least have some nominal value as skillful works of art, though I like the idea of the real value being the slug of weight in their bases. I'd add some coils of chains in the observation domes as a means for the corporeal undead to climb down and retrieve the bodies of any who fall to the traps below, which should go nicely with the skeletal remains in the kitchen (another nice touch). All in all, though, this seems like it's the best-designed of the pyramid's major levels. Well done, Hickmans.
I don't think the gauntlet should have any random encounters aside from incorporeal undead, so I'd use the same encounter list as the priests' quarters but with a bunch of empty entries. I'd definitely get rid of the tunneling gnome and just leave the connection between the entrance proper and the cavern to be discovered as a secret door. The contents of the cavern imply that it's been around for most if not all of the pyramid's existence, and its discovery should be a reward for thorough exploration rather than something to be handed to the players if they don't find it on their own. Frankly, I have a hard time believing a group would head into the gauntlet without going through the cavern first as the adventure is written (most likely just after killing the gnome, because it's beyond belief that the idiot would've stayed alive in this place for years with 4 hit points and a spoon), which would be the best approach for the most part, so making it blatantly obvious feels like too much.
As for the gauntlet itself, it was a letdown. I like the high priest's gimmick of being immune to direct damage, don't get me wrong. I think duplicating it with the gauntlet's first defense dilutes the idea, turning it from something special and impressive into an annoyance. The second defense might help the party more than it hurts them because it'd break the high priest's line of sight (unless the DM interprets them as one-way illusions, which is a trick that I was never fond of, personally). I also question how many people would actually be fooled by the second part of the illusion because "wall out of nowhere!" feels fake, but illusions always seem more obvious when you're reading an adventure than when you're actually playing it, so I wouldn't look down on someone for getting stumped by it. The third defense is nice in a vacuum, but it feels like it's being pulled out of nowhere. The fourth defense is just a boring fight against a sack of hit points. Also, it strikes me that the defenses are generally more punishing towards fighters and thieves than they are towards spellcasters, which just feels backwards. As I've said before, D&D games are almost always set in a world that should be fully aware that magic exists, so general defensive strategies should take magic into consideration. Not only does the gauntlet not do that, it's explicitly made easier by having a caster-heavy party because the clones can't use spells.
In short, the whole gauntlet needs to be reworked. First of all, there should be something in the priest's quarters to foreshadow it (as there is for the high priest himself), though what it'd say would be dependent on what's actually in the gauntlet. I'm fine with keeping the map (mostly to avoid needing to rework that as well, admittedly), the fourth defense can stay with the added effect that anyone struck by it has to save or be thrown into the water, and the clones can stay by disregarding their limitation against using spells and adding actual mirrors for them to step out of. Now, for the first two defenses, I'd want to think of ideas to inhibit progress (in a way that can't be defeated by flight, which would've clearly been a known effect during the time of the pyramid's construction) without handicapping the high priest and make use of the water, if possible, since that's the main feature distinguishing the gauntlet from a bare room. Since the gaze of an intruder would be drawn naturally towards the top of the corridor, a pressure plate that drops a portcullis across the walkways (maybe ten feet back from the landing) could be one option, though it feels like it needs a little extra spice of danger for anyone caught on the low side; perhaps a round after the portcullis falls, a pair of boulders also drop and roll down the walkways (extend the effect of the gravity trick in the dome of flight up to just before the portcullis to justify rearming the trap). I'd want a pressure plate there instead of the magical proximity sense of the other defenses specifically to vary how many characters can cross it before the portcullis falls. As for the second defense, if we play off of a body-mind-soul trinity here (since one defense is a physical barrier and one is a copy of yourself), the ideal choice would be some magical defense that tries to make intruders give up. An "emotion: hopelessness"-effect or "fear"-effect targeting any who cross the landing could be a quick and simple way of implementing this, I suppose, though it should be played up in a more flavorful way at the table. The point is to disrupt cohesion, delay the party's advance, and create chaos, and if the portcullis happens to be down, the clear path for retreat would be taking a ride in the water.
There are surely better ways of altering the gauntlet (taking a moment to peruse actual traps used in pyramids; real, mythic, and fictional; would be a good source of inspiration), but as with my changes for the random encounter lists and the maze, I'm just taking ideas off the top of my head for illustrative purposes.
Up until this point, I3 had been fairly good about not making assumptions about the PCs' morals, but the back part of the gauntlet is where that rears its ugly head, since it has both a required point of progress that's blocked to evil characters and a magical treasure that's harmful to non-evil characters. Since the latter is completely optional, I'm not opposed to it, though I'd prefer a creative curse (perhaps in the form of a geas imposed by whatever entity taught the high priest the secret of his gimmick) to simple level drain. The former, I'd just ignore; if a character reaches that point and answers the questions properly, they should be allowed to progress.
The water bed and the BDSM dungeon are silly, but they're harmless enough that I'd be willing to leave them in for a bit of tension relief.
Finally, after all the ordeals of the desert and the pyramid, there's the actual tomb of Amun-Re. It's a total anti-climax, but I'm fine with this, since rather than looking at it as a missing final challenge, I see it as a triumphant denouement. I wouldn't even try to punish the players if they slip up and reveal that they plundered the tomb on their way out, assuming they managed to break the curse, since that'd free Amun-Re's spirit from its purgatory and restore water to the desert. I would want to have some actual consequences in mind if the players try to speak divine names at the plaque, and I'd want to be prepared in case the players try to actually use the flying boat (who wouldn't?), but otherwise, it works well enough as a figurative capstone for the pyramid.
Oh, yeah, there's a fancy bit of prone written up as an ending, but it doesn't do anything that wasn't promised by earlier details of Amun-Re's curse, so it's just wasted space.
All told, I'm not sure if I like I3. Looking at just the pyramid (since the desert needs a lot of work to become a functional hex map), there's really just one level (the priests' quarters) that's pretty good as it is; the plundered tomb and the true tomb are more akin to single set pieces with a lot of window dressing (good window dressing though it may be), while the maze and the gauntlet both fail to live up to their names in interesting ways. Sure, I could use them as a shitty maze and a shitty gauntlet, but I could've done that much without the written adventure, too. I won't deny that there are some good ideas in them, but that leaves me more inclined to put those ideas into something else of my own design instead of following the adventure. That said, the plundered tomb and the true tomb do work as a good start and finish, and with enough good parts sprinkled between them to potentially offset the elements I dislike, I can see why the adventure has a good reputation, so I'm probably being too harsh on it overall. I don't think I'll commit to this being the lost desert tomb that I expect to need, but if nothing else, it can serve as a baseline to evaluate others against.