I just saw it. It was very good.
It fits very well in the niche it's supposed to occupy, and as Nut says, you find out a lot of details that are very relevant to Episode 4.
It reminds me of the latest Mad Max in that it fits very well into the Star Wars universe...almost as if the franchise has been boiled down to it's essence.
LOVED IT. Second best Star Wars film after ESB.
Only issue was the CGI was kinda... well yuck. Especially Leia. Tarken.. ok. But I an deal with that.
A lot of previews never made it to the movie.