I have not read Supergirl or Batgirl yet, but I have read the first three issues of Thor. So far, it is outstanding. Esad Ribic's art is heavily stylized but quite good, and the moody inking and coloring definitely fits the story being told. Jason Aaron's writing is quite strong. He's doing something highly experimental here -- telling a story that takes place 1,000 years in the past, with a very young Thor; in the present with today's Thor; and 1,000+ years in the future with a very old Thor. In each time period, Thor battles against a character called the "god butcher," who has been going around killing gods on many various worlds. Flipping back and forth between three different eras separated by thousands of years could be a story-telling train-wreck, and most writers would probably not be able to pull it off. There's a very real risk of the story becoming incomprehensible to the reader. Aaron, however, has done magnificently in the first three issues. The story is clean and easy to follow. The mystery of the god butcher's motivations and actions is tantalizing. And Thor's single-minded determination to track this villain and protect all the other gods drives the story forward.
As I say, I have only read the first three issues (I am about to head off to read issue #4 right now, in fact). But if the series continues to be this solid through all eight issues, this series is going on my pull list the next time I stop by my comic-book shop.
Note, I can not say the same for Captain America, even six issues in... despite the fact that I like Cap better as a character, what's going on in his comic is just... too weird for me. I am giving that one till the end of the first story arc (I'm guessing issue 8 or so) and if it doesn't get better, I'm done. But Thor is looking like a keeper.