Before we get the rants of how broken everything is, nothing is broken if everything is broken. I find this generation to be pushing the limits of our current metagame, and making the 5th generation's metagame focus highly on offense. Yet having so many swift and bulky sweepers i see this Generation focus on different aspects of offense and there will be more diversity and niches that Pokémon will fill. Just going to touch on some subjects, like bacon did, only i am not a psychic, so no predictions. :>
1. Sandstorm is as good as Rain/Sun now, Tyranitar is King.
With new users and inducers weather will be a force to be reckoned with. Yet the people who start to lay the ban hammer on Politoad and Ninetails has to realize now that Sandstorm is as potent as each. Not only is Tyranitar and Hippwodon bulkier than Politoad and Ninetails, they are coupled with a bunch of new sweepers that are to Sandstorm as Swift Swimmers are to Rain. Specifically Doryuzuu (Ground/Steel), and Landros (Ground/Flying), who both can abuse the sand (Doryuzuu base 176 Spe in Sand, access to Swords Dance) and coupled with Tyranitar can become a core to Sandstorm teams along with Rock Pokémon gaining a Special Defdense boost, importantly the Rock/Fighting legendary. Did I mention Sandstorm also does damage each turn?
2. The only thing that is broken is you.
"omg 147 base attack is going to break the metagame!!!! BROKEN! UBER!"
No, first off what metagame? 4th gen and 5th gen are completely different because frankly, one has yet to even begin. The 5th gen could have massive Mechanic Changes, this could be another Ramparados, we just don't know, but two Pokémon buzzing around forums are:
-Ononokusu is one of the over hyped Pokémon that are entering the scene, yet it is doomed to just miss the Awesome Sweeper bar. Paper Defenses, 97 Speed, nails in the coffin already, but who knows, it will have it's niche.
-Shanderaa is also seen as a Pokémon doomed to be scrutinized due to its dream world ability of Shadow Tag. I don't see how this is any different than steels were to Magnezone besides being able to trap everything, though it can't out stall Blissey carrying Toxic, it Is weak to Aqua Jet, it is screwed by U-turn and Shed Shell, some Pokémon will have to redefine their roles much like Salamances ban and the influx of Heatran. As long as Gamefreak isn't a troll, and this thing doesn't get Perish Song I am quite fine, this could possilby be the end to some Pokémon running Bands or running Fighting/Normal moves.
3. Whatever you want on your team could possibly flow well.
You could say this now, but running things like Altaria over Dragonite can only be backed up with the Different niches each occupy. With the Dream World plus new Items, there is promise that you could run anything you like because some niches are no longer overlapping between two Pokémon. Why run Crawdawnt? Adaptability + Dragon Dance + Rain. Why run Blaziken rather than Infernape? Speed Boost. Though this is a bit general (Caterpie + Magikarp Team!) Old Pokémon are now being put into the OU equation which could result in less overcentralization, but there will always be some centralization.