In the first movie, Evelyn is a clumsy and shy librarian, whereas by the time of the second movie, she has become a confident 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 ten year gap between movies.
Some people have accused the first film in particular of Protagonist-Centred Morality, questioning why Rick, Evy and Jonathan are the 'good guys' when they and the Americans are each digging up ancient treasures and ignoring local warnings. However, it should be noted that the Americans are all very self-centred, letting their workers take the risks and giving every sign that they'd keep the riches for themselves, whereas Evy was a librarian and historian who would have likely donated more standard archaeological discoveries to a museum even if she would have kept a percentage for herself and her team. In the end, Rick and the Carnahans at least believe they're only putting themselves at risk to satisfy historical mysteries, where the Americans put others in danger so they don't have to in order to satisfy their own greed.
Imohtep believed Evy looked like Anck-su-namun in the first movie because the eyes he took were from a man who wore glasses. Additionally, take into account Imohtep's reaction when he and Evy first meet in the first film - him peering at her in a manner implying he's trying to make out her appearance, and the questioning tone when he says Anck-su-namun's name.
Another idea is that, while she wasn't Anck-su-namun, Imhotep did recognize something familiar about her but just couldn't quite make it out upon being revived. The Mummy Returns then reveals its because she's the reincarnation of Nefertari, daughter of Seti I and Anck-su-namun's stepdaughter, someone Imhotep would've been around a lot when he was alive.
Why Evy lost her glasses in the first film: either they were completely superfluous, reading glasses, or she lost them along with all of the other supplies when the boat sank. Also would explain (if they were, in fact, reading glasses, as the film suggests) why it took her so long to translate the inscriptions of where the Book of Amun-Ra was and the inscribing required to make Imhotep mortal.
Some reviewers have criticized the way Imhotep makes so many mistakes in dealing with his enemies, such as relying on his fragile priests to attack Rick and the Carnahans, or how he killed the pharaoh in the first place. However, him killing the pharaoh was just a case of bad timing (the affair with Anck-su-namun was discovered and they had no other way to escape the consequences beyond the rushed plan to have Anck-su-namun take the blame and be brought back to life later), and in all later cases when Imhotep is fighting his enemies after his rebirth in the modern world, there is a simple explanation for his mistakes; Imhotep was apriest. He would have relied on his reputation and social standing to deter attacks on his person most of the time, but he wouldn't have had any actual military training or serious knowledge of hand-to-hand combat. After being brought back Imhotep generally relies on his powers to overwhelm his enemies, with the result that he never bothers to learn more sophisticated combat techniques beyond "kill them" when he's brought down to fighting hand-to-hand, and hence makes amateur mistakes due to a mixture of inexperience and over-confidence.
Pharaoh Seti's personality appears to be different in the flashbacks in the first two films, with the opening of Mummy depicting him as a jealous lover who desires 'control' of his mistress and the flashback of Returns presenting him as a loving father to his daughter. However, these views can be reconciled by assuming that Seti's personality is being presented "Rashomon"-Style, as obviously Anck-su-namun and Imhotep would have a different view of Seti's actions to Nefertari.
The second half of the first film has the rest of the Medjai bar Ardeth and Terrence Bay disappearing. Seems weird that they'd just abandon their leader and the heroes, right? Well, Ardeth Bay mentions to Rick and Jonathan not long after the formation of their alliance against Imhotep that the latter is impervious to any mortal weapon wielded against him. Ardeth also tells O'Connell that the rest of the Medjai were looking for weapons or methods that could hurt and kill Imhotep in the meantime. In short, having the rest of the Medjai to back up the heroes would have caused them to become a Red Shirt Army and suffer potentially horrendous losses against Imhotep, with no real way of defeating him.
It's often been mentioned that Imhotep's curse is really Cursed with Awesome, having a whole grab-bag of superpowers and "the glory of invincibility." But remember how important death and the afterlife were to ancient Egyptians. Being cursed to exist on Earth forever, with no possibility of entering the afterlife or even experiencing The Nothing After Death if your soul was eaten by Ammit, really would be the most terrible curse in the eyes of the ancient Egyptians. Basically, Values Dissonance at work.
Beni saved the world, this is not an exaggeration. I just realized after re-watching the trilogy. If you listen closely near the beginning of the second movie, you'll hear Jonathan say that the Spear of Osiris (the same spear needed to kill the Scorpion King) was a part of the loot that Beni packed onto the camels that he and the others rode off into the sunset with. Now think about that, had Beni not found that particular item and loaded it onto that camel, the whole world would have been subjugated by the Scorpion King and his army. Twisted but true, Beni's greed was the one crucial element to saving the planet.
Beni's mentioned that "this time" he has to take the guys who hired him from Cairo to Hamunaptra and back. Just how many people has he left in the middle of the desert to rot?
Imagine if the Medjai guards were quick to capture Anck Su Namun. They would have sentenced her to the Hom Dai for murdering the Pharaoh, an unforgivable crime. Imagine her suffering the same fate, and being eaten by beetles. But even worse, if Imhotep had tried to resurrect her following the events at the beginning of the film, he too would have been sentenced to Hom Dai. Imagine two almighty undead awakened. It is likely that the heroes would have failed to defeat them. And in the process they would have destroyed the world as we know it.
Eh, the Book of the Living was shown to render undead mortal, so in such a scenario Imhotep likely could have uncursed them both, sparing the world if not its factions.
Maybe, but that scenario is if the Medjai capture Imhotep before resurrect her, as in the movie itself. If they would resurrect in the 1920's at the time of the story, they would kill the ones that opened the chest, regenerating and bringing plagues and death twice. They would be caused an apocalypse already. Even if not yet, the curses would give them invulnerability, and immortality to escape death and stay together forever.
