This is really a continuation of many Geoff Johns storyline in the past few years. The main one is the Legion story in Action Comics. But he also revisits Superboy from Infinite Crisis and Sinestro Corps War, as well as the JLA/JSA crossover.
I am not familiar with the convoluted Legion history, but all I had to know was that there are 3 versions of them and they all come together in this story. They fight the perfect counterpart to their inspiration Superman: Superboy Prime who inspired the Legion of Super-Villains.
A lot happens in this story, including the resurrection of Connor and Impulse. Just for that, this story will be remembered as an important one in DC history. But the conflict with Superboy contains a twist about the identity of the Time Trapper. This being a time travel story, I had a lot of fun with it.
We also get to see the future of the Green Lantern Corps, which is obviously relevant for the current Blackest Night event.
The art by George Perez is perfectly suited for this type of story. Not only there are 3 full teams of heroes, but they’re actually 3 different versions of the same characters. That’s a huge challenge, but Perez has no problems with it.
This really is the culmination of many different stories, which is a bit weird since there are revelations about stories told in other series months ago.