Introducing a Brand New Feature in the Pokémon Video Games! Mega Pokémon.
And Yes, to answer any questions, I've been in the Pokémon series since it came to the west, since 1998, I've been a Fan, and have bought and played nearly all the games, which all the one's I have played are Fantastic(except for Battle Revolution). I have put more time into the Pokémon Franchise then all other Games I have played combined.
"In the Pokémon series up until now, there has been a limit on how many times each Pokémon could evolve. However, Mega Evolution is a different kind of Evolution, one that surpasses that limit.
Mega Evolution is described as an Evolution beyond all Evolution, a transformation found only in the Kalos region. It has also been called the greatest mystery of Pokémon.
In addition to far greater strength, Mega-Evolved Pokémon may also see their Ability change, or even their type!"
From Pokémon.com
To me it seems like an unnecessary attempt to add something 'new' to the series, while nothing but a complete overhaul could really make pokemon interesting again... always the same hm's ugh..
It's like they just added another saiyan level to dragonballz :L