Either way, after message boards were set afire last week with people trying to tell other people how to unlock Street Fighter IV characters, Capcom has posted up the actual, official methods. Once you have these two guys, you'll just need to beat the game with every character to get the final fighter, Seth.
As always, I recommend setting the game to Easiest and to one round if you want to make this process as short as possible. If you actually want to get better at the game and better understand how the different fighters operate, then stick with the default settings. I used to have trouble fighting El Fuerte players until I ran through the game with him myself. Now that I understand how his fast-moving stuff actually hits, I'm better at the game. And, really, isn't that the point? OK, less "stop complaining about unlockable characters" soapbox, more method. Here:
To unlock Akuma as a playable character:You need to get at least one "perfect" win in a round, and more than one depending on how many rounds per match you are playing.- 1 round match: 1 perfect round or more- 3 round match: 2 perfect rounds or more- 5 round match: 3 perfect rounds or more- 7 round match: 4 perfect rounds or more(including the last battle against Seth)To unlock Gouken as a playable character:1. Complete Arcade Mode playing as Akuma and watch (not necessary to watch everything) an ending.2. Then, unlock Gouken as an opponent, and defeat him.Necessary conditions to unlock Gouken as an opponent:- Play with any characters with which you watched the ending once (so play using a character you have already beaten the game with)- Do not continue at all.- Do not lose at all. Not even one round (easier if you only play 1-round matches)- Achieve certain number (or more) of "Perfect" rounds. The number of Perfect Win you need to achieve are:If you play on- 1 round match: 1 time or more- 3 round match: 2 times or more- 5 round match: 3 times or more- 7 round match: 4 times or more- Achieve certain number (or more) of Super Combo -OR- Ultra Combo Finishes. Super and Ultra finishes both count toward this number. The number of perfect win you need to achieve are:If you play on- 1 round match: 3 times or more- 3 round match: 5 times or more- 5 round match: 7 times or more- 7 round match: 9 times or more- Achieve certain number (or more) of First Attack (this means you must score the first strike in a match--the screen gives you the "First Attack" message, and you can mostly do this without even noticing):The number of First Attack you need to achieve are:If you play on- 1 round match: 5 time or more- 3 round match: 10 times or more- 5 round match: 15 times or more- 7 round match: 20 times or more- Then Gouken will appear. Kick his butt to unlock him!