What we heard....1 1/2 stars, too cartoony, all in all, not worth the $18 we paid to see it.
What we thought....I loved it. I loved the other two as well, though. So if you didn't think those ones were good, you probably wouldn't like this one. I was a little surprised they killed off quite a few of the main characters. Kinda like, okay, this is the last one. But then in the end, they left it open for the the possiblity of another.
The acting did get a little corny, but come on, it's a comic book. It supposed to be corny and cartoony. Special effects were good. Kelsey Grammer was pretty good as Beast, who I remember from the 1/2 hour cartoon (which I watched until I was about 20). I've never really liked Halle Berry as Storm, I've always thought they should have tried for Iman (David Bowie's wife). Everyone else was pretty well suited for the part they had.
Bottom line, if you liked the other two, you'll probably like this one. I don't know how true to the comic they stayed, because I never read the comic. But X-men was always my favorite comic book movie.