Evil ryu is Akuma, with slightly differents stats and different ultras, Oni is gouken, act like thier worlds apart sounds just as sad as COD fans acting like Black ops is completely different from world at war.
Gouken:
Different Normals
Fireball shoots in 2 directions
Has a palm thrust
Has some counter moves
Tatsumaki that goes upward
Uppercut is a super/ultra
Has higher health(I think)
Oni:
Different Normals
Fireball shoots in one direction, has 2 different fireball attacks(one being chargable) to compensate.
Shoruken is not a super/ultra
Has a claw attack that unlike the palm thrust goes through the enemy and you end up on the other side
Has a Ground Pound
Can shoot energy in the air that propels him in a certain direction across the screen depending on what punch button you push
Can do raging demon, on the ground and in the air(very situational)
Both of his supers are nothing like Gouken's, not even his fireball which does more damage up close and triggers a cutscene plus you can perform it in the air.
Easier to combo with
Has nothing else that Gouken has, no counters, upwards tatsu, or any uppercut super/ultras but makes up for it with his OWN MOVES.
Nothing you say about him being similar to Gouken makes any sense now that I mentioned their drastic differences. Yes hes a shoto, but a very unique shoto which you could also say about Gouken but that just further proves my, Rugal, and Kale's point that he is different. Anyway enough SSF4AE, I made a topic about it so continue this discussion in there since this is about UMVC3.
Edit: Also to me, comparing a CoD game to one another is like comparing one peanut butter brand to another, not much differences and not as much as Gouken and Oni's differences making the comparison between the two redundant.