POSSIBLE MILD SPOILERS, IF ANYONE CARES ABOUT THE MOVIE'S PLOT IN THE SLIGHTEST
Loads of fun from beginning to end, provided you turn your brain off. It's significantly more ridiculous and silly than the first, and doesn't spend too much time on anything that isn't either a) macho interactions or b) violence. In some ways, I think that it can be a little too ridiculous. But then again, that's what everyone is expecting. Although it's stupid, I think all of us really wanted Chuck Norris to be introduced in epic slo-mo, with the theme from The Good, the Bad, and the Ugly playing in the background... and that's exactly what happens. There are many excessively over-the-top moments like that. But if you pull out your inner 12-year-old boy and forget everything except how awesome it is to see Chuck Norris, Arnold Schwarzenegger, Sylvester Stallone, and Bruce Willis together in the same firefight, you'll have a blast.
And surprisingly enough, my fiancee loved it as well.