Finally. A cross-over between Street Fighters and Tekken characters! It's actually two games, not just one. From the OP in the Neogaf Thread:
Street Fighter Cross Tekken will be done in SFIV visual style with Street Fighter 2D gameplay.
Tekken Cross Street Fighter will be done in Tekken visual style with Tekken 3D gameplay.
So both will look and play different depending on the developer Capcom or Namco. The street fighter series is known more for flashy combo finishes and very stylized graphics. The Tekken series is known for it's in depth technicality of moves and side steps. It will be interesting to see what both companies come up with using the same character sets.
There is a crazy Comic Con video showing the first footage of Street Fighter Cross Tekken:
While I like both series, I don't think I'll ever be as exited as the people in the video.