For those who didn't like the first...

Rating: 7/10 (5 May 2001)

Quick and simple.
The Mummy 1999 - Bad scarab effects(and overused), bad acting (especially the female lead), annoying supporting acting, and a movie that was confused at times if it wanted to be serious or just fun.
The Mummy Returns 2001 - Cameo use of scarabs (darker and higher quality work), the lead actress learned how to act between films, the supporting cast did a much better job, and the movie was just overall more fun than the first. Oh yeah, the fight choreography was much better also.
Don't get me wrong, the sequel had it's problems also (nobody has been able to properly CG a human face yet, but ILM gives a good shot at it here)
What makes the difference between the two films is that the first allowed its problems to detract from it's overall quality, while the second has problems that just add to the "popcorn action film" feel.