I read the first volume of Y: The Last Man and did not care for it at all, so I ended up reading this just because it was loaned by a friend, and it is really good. The writing by Brian K. Vaughan is good although the characterization and ideas are nothing special but the world building is solid. It is really more fantasy than science fiction which is perfectly fine.
What makes it really excellent is the art by Fiona Staples. While in the North American comic book tradition it is informed by some of the more serious continental comic book art and is really good and distinctive. She has both a dynamism and a touch of magic to her art, which is very enjoyable, although her interpretation of a tree rocket ship could be better.
I intend to keep reading this and it was a nice surprise from what I thought was an overrated comic book writer.