Mega evolutions are so not necessary! Blaziken and Lucario don't need an upgrade in their stats. and I thought Awakened Mewtwo was just Mewtwo and his DNA giving him the power to change form, but it is just a Mega form -.-
They look cool, except for Ampharos, which is Dragon now, why?
Ampharos' Japanese name, Denryu, has 2 translations, it can either translate to Electric Current, or Electric Dragon (should be obvious when ya know that Ryu means Dragon).
So it was Elelctric Dragon in name since introduction, now it's elec/dragon in type.
UPDATE: The English Pokémon Youtube has uploaded a video showcasing the Mega Evolution in action!
It also shows the gym leader is named Korrina, and her gym puzzle involves using your roller skates to grind around the gym!
Also, the Torchic holding a Megastone has been confirmed for English distribution too!
https://www.youtube.com/watch?v=YTHgE0vtOXU
Also, Megastones are confirmed on the official site as hold items, and are named after the Pokémon that can use them, for instance, Lucarionite.
They can be found in game in hidden areas.
The official site also states that Mega Evolution lasts for the whole battle and then deactivates once the battle is over.
The official Site also has info on Super Training, which is accessed via the touch screen.