Hmm... perhaps I ought to go on holidays without Internet connection more often, as that seems to trigger CoroCoro leaks. Reading twenty-six new pages of what was a pretty quiet thread when I left is always a fun experience.
I must admit, Mega Evolutions were not a pleasant surprise. I especially dislike the use of the word "Evolution", and wished that the marketing department had used another word instead. But hey, nothing to do about it now. I don't particularly like it, but fact is that Mega Evolution, in concept as well as wording, is part of the Pokémon franchise now. Might as well accept that.
Yes, the Mega Evolutions do look over-designed. The old "rule of thumb" of Pokémon designs, that the design uses two colours plus black and/or white, seems to be trashed. Smooth lines and large, patternless surfaces also seem to be things of the past. At first glance, they also look overpowered. However, I think GameFreak will have a few aces up their sleeves preventing competitive battling from being centered around Megas.
Specifically, the "only one Mega Evolution per battle" thing, combined with the statement that other criteria than item holding have to be met in order to unleash the Mega Evolution. Perhaps you have to just have lost a Pokémon for the Mega Evolution to happen (like the boost criteria of the move Retaliate). Perhaps your team has to be "losing" (you have fewer useable Pokémon left than the opponent). I see a Mega evolved Pokémon more as a last ditch trump card, than an universally applicable strategy you can spam to win easily.
As for why they chose to reveal the Mega Evolutions they did... I think that was a carefully calculated move: Mewtwo is a poster child of Generation I. Those of us who played Gen. I definitely remember Mewtwo. Ampharos was a staple on Gen. II teams. Blaziken is very popular, the word of mouth would spread a lot quicker than if they had chosen Swampert or Sceptile instead (both of which I believe will get Mega Evolutions - through events, that is). Absol and Mawile both have a big fan following, and also signals that "no, we haven't forgot the unpopular ones". They are pretty obscure in the large picture, but were given attention along with the rest. It sends a message that not only fan favourites will be upgraded, we will be thrown curveballs as well.
By the way, the leak commonly referred to as "the Pokebeach rumour" mentioned TWO new formes for Mewtwo, the one we have not been shown was said to look more like Mew. I had a hard time believing this at first, but I think now that it's true, it's just that the leaker has assumed wrong: What he thought was a second Mewtwo forme might actually be Mega Mew.
Also, I agree with R_N, Sylveon is probably the only new 'mon related to old ones through normal evolution. GameFreak got a lot of flak for "messing with old designs" back in Gen. IV, and they might have taken that to heart. Mega Evolutions would be their new way of giving new relevance to old Pokémon, which might mean that we've seen the last cross-generational evolution in Sylveon, at least for some time to come. Here's hoping they will still remember the oft-requested ones such as Farfetch'd or Dunsparce.
Last, power creep. We all know it was bound to happen, it happens every generation. Though, I have enough confidence in GameFreak to believe they will spread the 'creep evenly, such that while Pokémon on average will be a bit stronger than before, their strength in relation to each other will be unaffected on a statistical level. Every generation, most Pokémon have been given tools that would have pushed them up a tier or two in the previous metagame. Yet Pokémon are still roughly as evenly distributed between the tiers as before, because the average power level rose as much as the individual power level. I wouldn't fear MegaBeedrill or MegaBeautifly and the rest of the NU losers sweeping OU any time soon, because their power level will still be lower than that of MegaQwilfish and MegaSlowking and other stuff in the new RU tier.
