I actually loved it, but then again I was probably in a very very small percentage of people that would hit their target on every front possible.
Jet Li/Jackie Chan - for fans of either, you get about the same amount of screen time, and both do a good job with their roles. Their "confrontation" sequence was, contrary to some reviews I read, very satisfying for me. Both provide a great mix of action and humor.
Micahel Angarano - I love him, he's absolutely adorable in every thing I've seen him in, but this was definitely his most physically challenging role. Not very well known, he may seem familiar to many people. He was Jack's son in Will and Grace, also starred in Sky High and Lords of Dogtown. He basically has to carry the "straight man" role in this film, and gets kicked and smashed around by virtually everyone. They trained him Keanu Reeves style and he pulls it off well. Plus no one does sad puppy dog eyes like he does.
Hot Asian Chicks - though I'm gay, I still love seeing hot Asian chicks on screen. So sue me. I saw Liu Yifei on a TV show briefly and really liked her. She doesn't get a lot of screen time here, but enough to make an impact. Very cute and I think she'll have a bright future if she decides to go the Zhang Ziyi route and mix English and Chinese films. For genre fans, she plays "Golden Sparrow" which was an awesome character made famous in some very old Shaw Brothers martial arts films. They even kept details like her weapons consistent (dual short swords), which I loved. Li Bing Bing plays an evil White Hair (modelled after, or maybe even the same character?) as the Bride with White Hair. I liked her a lot here as well, she reminded me of Halle Berry as Storm. Hope to see more of her too.
Story - a nice mish mash of martial arts genre films with plenty of homages paid to the genre, mixed with more myth/fable-esque stories based on the legendary Monkey King (of which I was a huge fan as a kid). Throw in some more conventional Hollywood-based grounding (using the Caucasian Angarano was a nice touch) and you've got yourself a much more accessible movie. Tone is more light hearted than some might like, but still remains faithful to the martial arts genre.
Filming - they did a lot of filming in China, and the on location stuff is gorgeous. Also some very nice martial arts choreography from the same guy who did the Matrix and Crouching Tiger.
All in all, a lot of fun, particularly for me personally. As someone who loves The Monkey King, old and new martial arts films, both Jackie Chan and Jet Li, cute Asian chicks, and adorable Michael Angarano all grown up and showing mad kung fu skillz, it had a little bit of everything for me.