I watched it without knowing what was awaiting me, assuming it to be a spin-off or remake of the old Mummy movies with Brendan Fraser and so I had pretty low expectations. It had some good parts and in my opinion never reached complete boredom levels, at least. I do have many complaints about the movie though. tl;dr version after long rant.
One big problem to me was that none of the characters were particularly developped. I didn't feel the main male character (Nick?)'s supposed development. It wouldn't be a huge deal if
the ending didn't heavily rely on him "realizing the good in him". No, he still felt like a selfish jerk to me at the end.. He was also extremely annoying throughout. I thought the mummy herself was the most relatable character, and the best parts of the movie is when she beats the crap out of Nick.
Another major issue is that it felt like they threw way too many different elements in there. Hallucinations, possession, a magic dagger, zombie-esque hordes, ghost-like apparition, mind-controlling spiders, AND DR. JEKYLL as a monster-researcher. They're obviously trying to tie a bunch of monsters together but this was just too disconnected from the main plot.
Lastly, the mummy herself. Don't get me wrong, she looked cool, her design was creative and the actress was right for the part. But does she have to be an erotic mummy, seriously? Kissing people to death, constantly making sexy faces at Nick and sitting on people suggestively when about to sacrifice them to Seth. If they want to make a sexy-mummy movie, ok, whatever, indulge in your mummy-fetish. But this was intended as an action/horror movie so it was just really distracting and unnecessary.
tl;dr: main character annoying, too many elements thrown in & mummy was hard to take seriously because of emphasized sex appeal.