I hope that health bar of dan is at 70% or something...lol...really hope gouken isn't overpowered... I'd love to make him a secondary to my ken. Fat shoto ftw..lol
Challenge mode isn't a good testing ground to see how much damage is dealt through those combos. Not to mention, a lot of those combos require Gouken to be at half-health or more, plus they're not that practical (seriously, a jump-in combo is great, but how often do you get jump-in combos?)
Gouken ranking on Prima's guide is probably pretty close. He's certainly beastly, and he is the most resilient of the shotos. But he doesn't really play like one. He doesn't have any cross-ups. Will lose in a fireball tossing match (all projectiles will beat his, unless he can fully charge). And while his air-fireball is decent, it's not that great of an anti-air.
His Hurricane Kick needs to connect high, or all hits will whiff, and he ends up pretty vulnerable afterwards. Further, it's not an anti-air move, lots of attacks will stuff it. His Palm Strike (horizontal Dragon Punch) is pretty awesome. EX version adds a launcher hit which doesn't lead to much unless in a corner (as seen in the video). Plus it goes through fireballs really easily. One of his best moves, and he's got a lot of them. His Demon Flip is awesome. His mid-air counter really helps his aerial defense and makes up for the lack of a good anti-air. His high and low counter can stuff several supers (ultras I'm unsure about), so long as they aren't projectiles, etc. And he has a few really nice command-normals that can lead to some nice combos. Overall, he's good, but no where near as powerful as some players make him out to be.
EDIT: Let me take that cross-up back. He actually does have a nice cross-up that can lead to his super.