Seth is hard at first, but he tends to have a pattern depending on how far or close you are to him. The best distance is maybe half the screen/jumping distance, cuz he just throws sonic booms or does his long arms. Just have to jump in and combo. But you can't stay in too close too long cuz he'll fuck you up with a piledriver or his ex kick move.
Game is pretty tight, i like it. I unlocked everyone except Seth. The grapplers seem overpowered, like Gief and Abel. It seems like throws got so much priority now, and the CPU spams it hard.
The new characters are kinda crappy. Capcom needs new designers =P I wish there were more new characters, cuz there's only 6 out of the 25.
In the end, the game is super awesome, but at times it feels like Super Mega Ultra Street Fighter 2 Alpha Plus: The New Challengers.