The story is simple, the action non-stop and the Yeti's very cool. Still, I enjoyed the previous two movies far better.
It's about twelve years after the events of the second movie and Rick and Evelyn O'Connell's son, Alex, uncovers the tomb of an ancient Chinese emperor (Jet Li) who was bent on world domination. The emperor killed all his enemies and buried them under the Great Wall of China. He's defeated by a witch (Michelle Yeoh), who turns him and his army into stone. The entire flashback recapping all this is great, though the "present day" interaction with O'Connell's interacting, bored, with their sedate life was, well, boring. Although Maria Bello does a good job replacing actress Rachel Weisz, she somehow seems older than Brendan Fraser, which is a little off.
The way they are able to say that the Chinese Emperor is a mummy is that he's still stone when he's resurrected and when it cracks off we see his rotted body beneath, so the stone is sort of like a mummy's bandages.