Alas, Poor Scrappy - Mr Burns in the first movie was a bit of a Jerkass (as were his companions, but it's hard not to be horrified as Imhotep slowly destroys him, and Evie's expression upon seeing his corpse mirror's the audience's feelings on the matter.
Crazy Awesome - The third movie abandons plot in favor of... whatever the writers felt would look really, really cool. Disappointing for fans of the other films, but a fine stupid action movie.
Greedy jailor digging out the gold scarab for himself? Predictable. Gold scarab turns out to be a real one and starts eating into him? Not funny. Greedy jailor inexplicably running screaming across the cave to smack into a wall? Funny.
Imhotep physically taking the American's eyes? Not funny. Imhotep winding up with the guy's astigmatism? Funny.
Fan Dumb - Many reviewers and other people did a great deal of smug snarking about the reference to metal being one of the "elements" the Dragon Emperor could control, seeming to believe this was some moronic error on behalf of the writers since it wasn't one of the four standard elements in western mythos. However, Chinese mythology does regard metal as an element, meaning that it was one of the things the filmmakers got right.
Fridge Brilliance: In the first movie, Evelyn is a geeky, clumsy and shy librarian, whereas by the time of the second movie, she has become a confidant warrior and a master of swords and guns. While some may find this a jarring change, if we consider what she's been through, along with her choice of husband and lifestyle, it's a very believable change for the 10 year gap between movies.
One of the deleted scenes in the first movie involves a pair of zombie priests digging out the Book of Amon-Ra before Rick and Johnathan can get to it, wherein they're sprayed with the same acid that killed the group who unearthed the Book of the Dead. Why delete the scene? Because no doubt the Egyptians would not have wanted to make it as hard to kill the creature as it would have been to release him.
Fridge Logic - When the scarabs are poured over Imhotep, they appear to begin devouring him gradually, a fact which Evelyn later confirms, stating that the beetles devoured a corpse "very slowly." However, whenever the scarabs devour anyone else later on in the film, they do so almost instantaneously, as shown when Beni falls victim to them.
Well, they had been in an ancient temple for a long time with probably nothing else to eat. Maybe they were just really really hungry?
Different breed of Scarab?
It's outright stated several times in the first movie that the curse used on Imhotep grants the victim invincibility and lots of cool undead superpowers should they ever be dug up. Given this, why did they bother using it on him? Granted, that was apparently the only time they used it, since apparently the curse was horrible enough that it hadn't been bestowed before, and he does suffer the whole "eternally chewed on by flesh eating beetles" thing.
Well, think about it. The Egyptians were big on the afterlife, they spent massive resources trying to reach it. By making him immortal, they're basically DENYING him rest, forever. He can't die, period. Any death is just temporary. So, he has no chance of reaching the afterlife, which for the ancient Egyptians would've been a terrible curse.
Alternatively, the point was to dissuade anyone who might otherwise choose to bring him back. It was the Ancient Egyptian equivalent of burying him with a crate of land mines.
How the hell does the pharaoh's wife scratch an itch or go to the bathroom? And what about sitting or eating? I mean, the smeared paint could mean she just got itchy or something dammit!
In the Mummy Returns, Imhotep scares the bejesus out of a trio of mercenaries seemingly For the Evulz. What does Meela Nais tell them to do? "Openthechest!" But if the chest was lost when Hamunaptra sank, where did they get it... and where did Imhotep learn English?
The Medjai know damned well the Egyptian gods are real and their curses work, and exist only to fight the monsters they left behind and prevent their rise by any means necessary. How were they ever converted to Islam?
Hilarious in Hindsight: In Hero Jet Li is trying to kill the first Emperor of China. In Tomb of the Dragon Emperor he is the first Emperor of China.
Large Ham - Damn near everybody by the second movie.
Sequelitis - The Scorpion King 2 is a prequel to a prequel to a sequel to a remake of a movie from the 1930's. Wheras The Scorpion King 3 is a sequel to the first Scorpion King film, which in fact was the prequel to a prologue of a sequel to a remake of the movie from the 1930's. Head hurting yet?
The subsequent finishing of the job...*Dies A Little Inside*
Ankh-Su-Namun's betrayal of Imhotep at the end of the second movie.
When Horus got killed.
They Changed It, Now It Sucks: In the third movie, where Evie's actress was changed. Some fans of the original were very disappointed in this. Justified in that Rachel Weisz was just recovering from her pregnancy at the time.
Plus, she reportedly turned down the film after a brief look through the script.
Visual Effects of Awesome - The first two films feature some great special effects work. The third however, to a much lesser degree due to moments of fairly jarring Special Effects Failure, specifically Jet Li's character transforming into King Ghidorah as well as his character beheading someone earlier in the movie.