Blissey's never been particularly hard to deal with in 4th Gen, and with all of the new contenders, especially a SPECIAL ATTACKER (one that doesn't even get psycho shock) that apparently warrants a move slot (or two) just to deal with, I don't see Blissey being too great anymore. There's also the meta leaning towards physical offense instead of special offense (outside of Shanderaa and some others like Starmie) making it not as great. Blissey's still a good Pokemon and all, but she's just not amazing anymore.