Megas are a wonderful idea that will add depth and change to this series, which it desperately needs.

The only reasons people think they are a bad idea are
>muh childhood
>muh metagame
>muh over-designs

When really, none of those are problems at all. If anything, the metagame was always flawed due to the amount of limitiations put on it by smogon, in addition to the fact that you could never see the EVs or IVs. Keeping a mental track of them was even more autismal than doing a Nuzlocke playthrough. The fact that they are now visible in X&Y makes this the first Pokemon game that's actually playable competitively.

Also, fuck your childhood and your idea of designs. Most of you probably visit /a/ or /mlp/ anyway so your idea as to what constitutes a "good design" is completely irrelevant.