>>187696571. Bad distribution: a lot of Pokemon that got Megas did not deserve them. Garchomp, TTar, Gengar? Fuck no. Plus giving Blaziken a Mega and the other two Hoenn starters fuck all.
2. Some Pokemon would have been better with just an evolution, sure it makes sense for 3rd stages, and some Pokemon like Mawile benefit from taking advantage of Intimidate before Megavolving. But M-Banette is shit because it can't take advantage of Prankster until the second turn, and has fuck all for defensive stats. Things like M-Manectric and M-Houndoom would have benefited more from an evolution so their speed wouldn't have been gimped turn 1.
3. Design wise, they're shit. Most of them just look like their base forms with more spikes/ornaments, and while some I think are improvements (Charizard-Y) they're not very creative and just seem lazy.
4. They're literally designed to be game-breaking. They basically chose the most broke-ass abilities and pumped up their best stats. Things like M-Gengar and M-Blaziken should have been obviously noted as incredibly stupid before release. The only saving grace was that they can't hold any items, thus preventing a lot of things that would be Choiced from wreaking havoc.
5. One per file version exclusive megas? It's like GF wants cloners and hackers.