Before I say anything about this comic, the only Legion of Super-Heroes I know or care about are the ones from the current series. I know there have been at least 3 different teams of LoSH, but the only ones I am familiar with are the ones from the current Legion books. So with that out of the way;
Overall- The initial issue of this series dealt with one of the contingents of the Legion that I was unfamiliar with. They were apparently the ones who gave Superman his Legion Flight Ring. Apart from the Legion's troubles with politicians who wanted them to disband, Superboy Prime was transported to the 31st century, and after visiting a Superman museum in Smallville, was enraged to find that his statue was located in a isolated corner of the museum. Apparently, the museum curators didn't think much of Prime, which drove him into one of his characteristic rages. Before destroying the museum, he learned about the Legion of Super Heroes, and decided he would destroy them out of his spite for Superman. Prime travels to a prison planet, and releases every super powered criminal there, with the promise of killing every last member of the Legion, thereby eliminating any trace of Superman's influence on the future.
Back on Earth, the Legion learned of the threat of Prime, and transported Superman himself to the 31st century to help them deal with Prime. Brainiac 5 also said that it might be a good idea to call in members of the Legion from other dimensions. Superman agreed to help the Legion, stating that he wouldn't stop until Prime has been redeemed, believing Prime to be a good person deep down, gone insane. Considering the horrible things Prime has done, I'm not so sure he's redeemable, but Superman is ever the optimist...
I liked this story, even though it didn't deal with "my" Legion. The fact that Geoff Johns was the writer sure didn't hurt matters either. For a score, I'll give this a 7 out of 10, but I can see this series has the potential to become either something really lousy, or unbelievable great.