A major update to an already popular fighting games proves to be pretty well, despite the fact it wasn't needed.
The New Challengers to enter Arcade Edition include from Street Fighter III, Yun and Yang. The twins make their presence felt in the Street Fighter IV world, delivering a very strong offensive rushdown character in Yun, and a more technical defensive/offensive character in Yang. Each character boasts an arsenal of special attacks that can frustrate opponents who don't know their match ups pretty well. Although they play minutely similar to their 3S counterparts, the world of Street Fighter IV fits them pretty well.
The other two available characters are Evil Ryu, and Oni. E. Ryu is of course the concept of which Ryu succumbs to the Satsui no Hado, or Murderous Intent. He's an even blend of both Ryu and Akuma, with a set of moves that can leave an opponent stunned very quickly. E. Ryu can deliver massive damage to his opponents, but as such can also be a defensive character. His only weakness is his stamina as he takes a lot of life loss like Akuma. Oni on the other hand brings something a little more unique. He is the ultimate demon form of Akuma who does have a fireball, a dragon punch, and a hurricane kick to boot, as well as a slash special that can cross your opponent from the ground. He also has an air dash that can act as a bait for anti-airs and a counter hit if it connects. If played right, Oni can be a very disturbing and annoying character to fight against.
As for the original 35 characters, they have been updated quite a bit to further game play. Such re-tweaking took away certain abilities, but also gave them newer stuff. An example of this is Cammy. In Super, she was able to do a normal instant cannon strike from the ground, allowing her to build meter from a distance incredibly quick. In Arcade Edition however, they took the instant cannon spike away from her as it now has a height limitation. Even though that was taken away from her, they buffed her normals, so now her combo potential is much better, and she still builds meter incredibly quick. Other changes seem to do worse for the characters. Guile's Ultra 2 originally did 420 max in Super. In Arcade Edition however, it was nerfed to 300. I'm not sure why Capcom did this, but if it was intended to balance the game out, they probably had a reason.
What's also new for this game on consoles is the replay channel, as it has been revamped. Players can now follow up to five online players and see any new replays they have uploaded. Say for instance you want to learn how one player plays your character, you can follow that player and see what he does in matches against other opponents. There is also an elite replay mode which if you have over 3000 PP, you can upload a replay to your own liking.
The last thing is now you can search for replay channels that are now available. If you have a friend whose doing nothing but showing replays in his channel, you can search his channel by entering his SN and then you can join in.
Other tidbits include the online mode and endless battle lobbies. You can now create an endless lobby room with a name and have other players join you from both the Super and AE networks if you bought the game via the PSN. If someone owns Arcade Edition, but your friend owns Super, whilst you're in endless lobby the game will automatically switch the player that has AE back to Super for battles and such; this way people who don't have Super but want to see AE battles can still do so with ease. When you go back to Super, the four new characters will not be available for use so keep that in mind.
All in all, Arcade Edition is a nice update that isn't necessarily needed, but if you want to be up to date with the current Street Fighter IV game, it's worth a purchase. Like I had mention, you have two options to buy this also. If you own the original Super Street Fighter IV Disc, you can purchase the game via download through the Playstation Network, or if you want to have the disc based game only, you can also buy the disc instead which will retail for about $40. If you download the patch however, you can choose to go back and forth between Super and Arcade Edition via the options menu, which is key for endless lobbies. If you're looking to up your game in the Street Fighter scene, this would be a great add on.