I'm happy with a female Thor as long as:
1. There is a reasonable plot explanation about how she changes gender.
2. She's not wearing a sexy/tight outfit.
3. The essence of her character's personality doesn't change
I agree the story needs to make sense, the idea won't be embraced unless there is a real and logical (in terms of comic book superhero logic) story to follow.
The outfit will likely be skimpy/sexy, the comic book world is taking baby steps in the right direction but ditching scantily clad female characters would be a giant leap. Here is the concept art for the new Thor: http://time.com/3001549/marvel-thor-female/
The amount the character's attitude changes will likely depend on the story arc the writers take. There will likely be some changes in the persona but hopefully they can remain true to the world that surrounds Thor as a character, if that makes any sense.