In the future, Superman is a worldwide celebrity that is praised universally as the greatest entity to ever lived. Though with his presence long deceased, and evil running around without a single hero able to match its strength, the Legionaire fly into the past to retrieve Superman. Unfortunately they went back a little too far when he was still a teenager, before the world even knew Superman existed! However, it was something they had to work with. The Legionaire, adding its newest and most important member Superman, save the earth in its future from various natural disasters and enemies.
It almost seems like with Teen Titans ending its legendary run, they had to animate another big name superhero, and who better to centralize a cartoon with than Superman? The show does everything that Teen Titans has basically did except with different characters and in a more universal (literally) setting. That's not a setback however; Teen Titans was a good show and copycat programs aren't anything to dog a cartoon on unless it copied another show while doing a poor job of it. Legion of Super Heroes has good execution.
The problem with this show really dwells within its characters. There was never really a point where you have a connection with them. They just feel like these vessels on a daily cartoon show exchanging blasts and punches with its enemies. It also has a very weak supporting cast; many of these random superheroes are often introduced with almost no background for us to know more about them. The only thing we do really know about these extra superheroes is their names and powers. A lack of real character development within both the main characters and its supporting cast knocks a lot of points off for this show.
Plus the lack of a major antagonist establishes Legion of Superheroes a show to watch whenever it is on. Most of the individual episodes concerns a very non threatening villain with a predictable ending to how they are dealt with. The antagonists are just as important as the main characters, and it is pretty disappointing to see that there really isn't any inspiring villains in this entire show.
Still a pretty solid show despite its setback of any real character development, though sadly the characters are always the best part of a show. You can have a bad storyline and some wonderful characters and it can still be a classic. Still, if you have some extra cash or time, Legion of Superheroes isn't a bad choice, but it's not good enough to really go out of your way to get or watch.