>>19677760They form a really nice starting mon to build around and make things easier for newer players.
You can take multiple possible megas on a team, making it necessary for the opponent to try and work out which you will use. You can even give them Mega Stones, but this becomes a tactical choice as only one can Mega.
The decision on when to Mega is significant for many pokemon, as it can lose them a useful ability. I've had a lot of fun against Rain teams by simply not letting my Charizard Y go Mega, causing the opponent to waste switches and Rain Dances.
Some Megas are extremely strong, but the nature of Doubles smooths it out and GF doesn't design pokemon to work in competitive Singles anyway.
I like them. I really do. It even provides an opening for GF to provide multiple evolution lines without clogging up the Pokedex even more; just because Mega Alakazam is a bit shit this gen, doesn't mean it won't get another Mega later to buff it or let it do a different job. Lots of new design space in a game that really needed it.