...why does no one care about Gengar? I think he'll be a huuuuge format breaker because of Level Down, which is an ability we have not yet been introduced. Level down mean it laughs in Arceus' face, and owns Salamance so hard it's going to cry at the 2HKO with Level Down. Fainting Spell also spells "death" for most decks, especially since SPs are gone, which means Skuntank G is as well.
Tangrowth will see a lot of play as well in my opinion, and will make Gyarados completely obsolete. Tangrowth loses to Charizard, though, who I think will see a good amount of play just by itself.
As for Salamance, he isn't hyped enough. An energy every turn with Delcatty? Uh, yeah, that sounds good. 2 prizes? lol better. And if Expert Belt does see play, that's 4 prizes, again a mechanic we have not yet had introduced.
Arceus isn't very good, let's get over it. Gengar walks alllllll over it, and so does Machamp. FlyChamp will still be around for Salamance, although it'll be interesting to see how Salamance will tear its face in half.
Speedrill is alright, I guess it might see play. Not as much as it does now probably.
Tier 1:
Gengar
Salamance
Flygon
Tier 2:
Tangrowth
Charizard
Beedrill
Tier 3:
SP Decks
Arceus
Gyarados
Tier 1.5 is kinda redundant in my opinion :X
Anyway, that's how I personally see it. I don't see Arceus making a huge impact on the metagame, but, who knows.