I was expecting to really hate it but instead loved it. I thought it was flawed, yeah, (I'd like to have seen a from-scratch version rather than a sequel), but I really did enjoy it immensely.
Remember that moment when (SPOILER) he landed the plane in the ball field and the crowd looked stunned for a few seconds then jumped to its feet and went wild? That's how I felt. I didn't realize how much I'd missed him while he was gone, you know?
And I wasn't alone. Several in the theater cheered aloud at that point---how often do we get to see that happen?
As for the character being "boring" or having unclear motivation, I disagree. I think it is refreshing (and inspiring, to be honest) to have a character who acts for altruistic reasons. What's so unbelievable about someone doing what's "right" just because it is the right thing to do? Especially when it is organic and true to the character, given his heartland upbringing?
A character doesn't always have to be overcoming a horrifying childhood or lifelong mistreatment for me to identify and be inspired. (Though I love those characters too, as long as they aren't too predictable. While I'm sure the film will be great, I was annoyed by the Spider-Man 3 trailer and the way the story will be focusing on the "how long can a man fight the darkness without it getting inside him" thing. Hero corrupted? Done to DEATH, I think...)
Plus, I really enjoyed all the Father/Son/Savior stuff that was made so clear in the film. Some may cry "sacrelige" (I work with someone who has), but I thought it was an enjoyable element that isn't always brought out (or done well) with the Superman stories. Nice to see that part of the mythology acknowledged. (But then I'm a sucker for a good Christ allegory...or Gilgamesh if you prefer)
So, yeah, I didn't like Spacey's overcooked Hackman impression (or the choice of Lex as the adversary in the story), and I thought the final crisis was too drawn out and predictable, but I was very pleased overall.
Worth seeing, I'd say.