Just got back from seeing it...
Overall, a big improvement over the first. Its fun, doesn't take itself too seriously(just like the FF comics), and has a good sense of humour with some great action. The Silver Surfer was done great, and I hope the rumours of him getting a solo movie turn out to be true.
Yes, him turning around at the last second was kind of odd...but that is what happens in the comics. He's taken Galactus to world after world and its only when he meets the FF that he turns around. Of course, in the comics he gets banished TO Earth, but still. The sudden turn around for him is how it should be.
Power swapping was played for good humour and a nice Super Skrull nod without all the baggage. They did mention it had to do with the same kind of cosmic radiation that gave them their powers, thus giving a not-so-technical explanation for 'why' that drove the other thread on for so long. Wasn't similar in the comics, no, but it is here.

As for the power swapping killing Sue...there wasn't any indication that it put a strain on them, just a surprise the first times it happened, so it wouldn't have hurt her at all.
The only two problems are Sue and Galactus. As everyone has said, Jessica Alba is just not Sue Storm. They wrote the character right, she has the perfect attitude to BE Sue, but the actress behind it just plain isn't. The worst part of it all is the nailed the casting for the rest of the FF perfectly.
Galactus...well, he wouldn't have been so annoying if Marvel hadn't had people say multiple times that we'd see more than a cloud. Arguably, we did. There were hints of the classic shape of him here and there, including at the very end with the fire inside in an almost-Galactus form, but its just not the same. Have to admit that it wouldn't be a problem with me if the Ultimate Alliance game hadn't done a realistic looking Galactus so damn well and showed it could be done.
But beyond those two things...its good, quirky FF fun. Yep, its cheesy and really out there with science things...but that's the FF and how they've always been.