The series is split into Volumes and Seasons. There is 4 seasons and 5 volumes.
Season 1 - Volume 1 "Genesis" - 23 Episodes
Season 2 - Volume 2 "Generations" - 11 Episodes
Season 3 - Volume 3 "Villains" - 13 Episodes
} Season 3 - 25 EpisodesSeason 3 - Volume 4 "Fugitives" - 12 Episodes
Season 4 - Volume 5 "Redemption" - 19 Episodes
I can't really say much about each season as most of the stuff would be spoiling it as there is many twists and deaths ;P.
Here is what happends in the couple of episodes of the first Series.
"In October 2006, people around the world discover that they have superpowers. High school student Claire Bennet finds herself spontaneously regenerating. Heroin addict Isaac Mendez can precognitively paint future events, including a nuclear explosion in New York City. Japanese office worker Hiro Nakamura is able to teleport and time travel. Nurse Peter Petrelli experiences visions that convince him he can fly. Indian scientist Mohinder Suresh travels to New York to continue his recently deceased father's work by finding these people. A mobster named Daniel Linderman sends two men to Niki Sanders's home to collect a loan that she has not repaid. Niki blacks out and later finds the men dead. " -
WikipediaI'd give this a rating off 9.5 out of 10. It is one of the best TV series I have ever seen but because of the intensity that is built with each character it gets very annoying how something dramatic will happen to a certain character and you won't know what happens next until the next couple of episodes.
F.
