Good Ryu players don't backflip into his Onigyn(sic) stance.
Most players who use the stance, tend to use the teleport attacks, of the three, two of them are linear and can be stepped. The other, the throw, can be ducked. Since you can pretty much see it coming, the idea is to step or duck. Usually the players will be pretty obvious when they do one or the other (and fail).
Other attacks from stance include a high elbow attack (ducking or stepping works), the low slide (stepping or guarding low), and the three hit strike. The three hit attack is mostly combo filler, but the hits track. Still they all hit mid and can be dealt with if you just block and hold the final hit (which can also be stepped).
Ryu's overall stance isn't bad, but it isn't good. Good Ryu players will make sure that the stance transitions are invisible before they mix them up. The really dangerous stuff is a three part throw and a special teleport hold that can lead to some nasty stuff. Otherwise, its fairly manageable - though annoying - to deal with.
