I am a HUGE fan of the first two mummy movies so I rented the third. I didn't expect too much because the whole crew changed and Stephen Sommers didn't even direct it. As a movie it is okay but not great, and it would have been much more acceptabe if it was named something else not having to do with the Mummy movie series since it has little to do with the first two and the only original remaining actors are Brendan Fraser and John Hannah.
It depends on what you look for in the movies. I mean, if you are an Evy or Alex fan, don't waste your money, but if you are a Rick or Johnathan fan, you would probably enjoy it, not as good as the first two though. Imhotep and Ardeth aren't in it though.
I, personally, liked it. But if you're looking for something twice, or thrice, as good as the first two films, most likely you shouldn't watch it. But if you do want to watch a fun, and fairly well entertaining movie, you should watch it. But don't have high hopes or have too high expectations. Because it'll ruin the whole movie for you.
You also shouldn't compare it to the others so much, either. Expect to see new bad guys, good guys, and some yetis.
Uh... I had to get used to it. It doesn't have anything to do with Egypt (obvsly, but some people might not realize that), so it doesn't have Ardeth or Imhotep or Anaksunamun or any of them. Rick is a little bit different, mellower, I guess, but still great. Jonathan's as big of an idiot as ever, and IMO the best part of the movie. Evy's played by someone new, I don't know her name, and she wasn't that great of an actress. Alex... meh, I didn't like him.
Put it this way: don't compare it to the first two, and it's pretty good.