Was it the designs?
Was it how it improved upon or changed the pokemon who received it, ability or stat wise?
Was it the lore or implementation?
Was it how it affected the meta?

Why is Mega Evolution awesome and why should Game Freak keep it?

For the record I do agree that Mega Evolution does have some significant flaws and a few of the megas went to pokemon who didn't need it or were already powerful. However, you'll never really fight the legendary Megas aside from the latis unless you deliberately go hunting for that ballpark and the vast majoirty of of them did go to pokemon who were either neglected or popular but terribly weak. I understand why some people have gripes with it, but I hope for game freak to focus on it more to iron out those issues and help other pokemon up like they helped most of the ones here.

Personally I'm a fan of the megas who completely change how the pokemon in question plays and/or drastically alters it's playstyle, like Mega-Saur becoming a bigger jack-of-all-trades compared to Chlorosaur, Pidgeot becomes a dedicated special attacker instead of a weak physical attacker, or how Aggron becomes a bulky behemoth compared to the Head Smash spamming Wallbreaker that is it's normal form.