In particular, I think having Groudon released in the winter is extremely unlikely, since they're trying to push the weather thing. My money is on a spring release of Kyogre, and summer release of Groudon, if anything.
But about Slaking--who else is pumped for another fat normal type in every gym? At least his bulk is more like Snorlax than Blissey... And I'm hoping they balance his crazy attack with Slack Off sufficiently.
Edit: and about the other good 'meta' pokemon, I'm also surprised that they might give out so many. But notably, Metagross is the only one that'll really shake things up (no double weaknesses, super high CP) and they'll probably hold him back for a while--they wouldn't want the snow bonus to make him too common and flood the market with high-IV ones.