Season 1 - Very cutesy with a child-like demeanor to it. Signs of the Brony Fandom come late in the series and are very minimal. Season 1 is the most innocent season so far.
Season 2 - Integration of Pop Culture and Brony Fandom are on the rise. The innocence is still there but is mixing in with the references (Not to say that there weren't any in Season 1 though). While still retaining innocence, it is starting to be less like a child and more like a man.
Season 3 - Full integration of Brony Fandom comes around full swing. Fan Favorites such as Luna return with bigger plots explaining their past; Derpy Hooves comes back from the fires of Consecutive Meddling to have an entire episode dedicated to her; Trixie and Gilda come back to ask for forgiveness and explore their history; and the show goes deeper into love having an episode centered around Lyra Heartstrings and Bonbon. Series is also taking a darker turn. While still remaining cutesy and fluffy, they tackle bigger issues that sometimes even a Friendship Report can't solve.
The Movie - An epic story with an epic quest. Equestria is put on the bridge of death (again) and its up to the Mane 6 to repair what was damaged before things become permanently dead. Other side notes to be included are the spirits of Nighmare Moon, Discord, and the Windigoes team up together for a showdown with the ponies; all Alicorns in Equestria are taken away and locked up for safe keeping; the Diamond Dog's return and reason why they require many gems (Long story short, it's epic); Big Macintosh and Cheerilee finally proposing to each other; an all out war breaks out in Equestria; the Cutie Mark Crusaders finally find their Cutie Marks, and the Mane 6's friendship along the trip soon evolves into a six way 'Friendship with Additional Love and benefits'. Due to the surge of the Brony Fandom at this point, Hasbro's slick marketing to make it even appeal to even the deepest of haters, raving high-scoring reviews by the critics, and high DVD sales afterwards soon puts My Little Pony: Friendship is Magic as one of the most influential animated series of all time. It is tied up there with the Simpsons at this point.
Spin-Offs - Due to Hasbro's great influx of money and wealth from the Friendship is Magic series, they decide to exploit (In a good way) the rise to stardom. They even go for the darkest and edgiest approach possible to draw in more crowds To help combat TV's hour long critically acclaimed series, such as House, Breaking Bad, and The Walking Dead, Hasbro funds to make the widely praised and well know fanfiction, Fallout Equestria, into an hour long program that will run on AMC, directly competing with the other big shots. It is well praised for its fantastic animation, gritty and taboo subject matters of something so childish handled like an adult done extremely well, and being very faithful to the story while being an amazing TV series adaptation. Past Sins also receives this treatment in the form of a two-parter movie. The ponies also get themselves an RPG video game developed by Bethesda Game Studios and even an FPS done by Valve. Both were critically acclaimed and sold well, and with the latter being Valve, a HUGE surge of Source Engine ponies coming about.
The History of Friendship is Magic is amazing, isn't it?