Guardians of the Galaxy. You have to admit, it's very ambitious for Marvel/Disney to go forward with this movie. It might just be me, but it could be a harder sell for the non-comic book reading moviegoers. This is going to be a movie most likely not featuring any characters that are household names. The average person will not know who these guys are. They'll know it's part of the same movie universe as The Avengers but will that be enough of a sell? The fact that it's sci-fi puts it in another film genre.
The key will be the casting. Today it was announced that Marvel has a short list of actors for the lead role of Peter Quill, aka Star-Lord. According to Deadline, the actors on this list include Joel Edgerton (Dark Thirty), Jack Huston (Boardwalk Empire), Jim Sturgess (Cloud Atlas), Lee Pace (Lincoln and The Hobbit) and Eddie Redmayne (Les Miserables).
It's not clear if these are the only ones being considered. Personally, I'd love to see Jim Sturgess in the role based off this list.