There is no singular approach to Mega Evolution design, which is what makes it so compelling to return to. Each of them is exaggerated, but in a completely unique way. You might moan about Megas like Garchomp or Tyranitar having "spikes everywhere" (they were edgy and aggressive in the first place), and then completely ignore the more elegant designs like Pidgeot, Ampharos, Altaria or Gardy. Or Kangaskhan who doesn't change at all and instead fights together with its child. Slowbro also doesn't change, but the Shellder evolves a second time. It depends entirely on the species.