the OU metagame feels like you have to make a team that is either super-offensive, or super defensive. balance just isn't there anymore.
it got all screwed up with the introduction of drought and drizzle on terrible pokes. The metagame has become a fight to win the weather war and how you take advantage of it.
eviolite hasn't done anything to shake up the OU metagame really, chansey is more of a poor man's blissey, porygon2 is a situational counter, no one else matters
air balloon adds some elements into team development but really, it's more of a good gimmick than anything (although it's really good on heatran)
but really, it's the weather that defines the metagame, you pretty have to make sure your team consists of politoed/tyranitar/ninetails and then support for them (hippowdon just isn't good enough to handle the weather switching and hail is by far the worst weather). you can make a weatherless team to be effective but when doing so, you have to make sure your team can survive in a weathered fight (as in, can it take advantage of sand, sun, and rain and how do they do it?) there's always going to be something anti-metagame to pop up (like lead machamp in Gen IV) but really, the closest we have is multiscale dragonite, but he's better at abusing weather than being the anti-metagame threat
i just feel the metagame isn't as unique when it comes to team building, like there's a big gap between top OU pokes and the less OU pokes, unlike in gen IV.
don't get me wrong, with a good team, it's still fun, but it feels way more centralized than gen IV did.