Greatest thing it could have done to appeal to mainstream audiences was that it simply gave an INSANE amount of characters on RELEASE. So when you paid $59.99 for it, you got the complete game (except Tekken 1-6's soundtrack). At launch this game had more characters, more stages, more moves/character, best netcode (after skullgirls), and fantastic balance accross the cast of characters over any other fighting game in history (Well, KOF2002UM and MK:A had more characters). Nothing like P4A/KOF/BB making you pay for glasses customizations and colors and a massive far cry from the Capcom games DLC where they charge so much for a single character.
The fact that this customer friendly gesture wasn't enough sets an unfortunate precedence and I fear the last fight game bastion that didn't rape their customer's wallets has pretty much crumbled down.
And this is even before talking about the raw gameplay and tag mechanics they introduced in TTT2 which is so well done I struggle to think of ways it can be improved.
And for the people who were scared of the tag mechanics, Namco supplied a solo mode just for you guys.