If it's a rock solid 30 fps, it won't kill the game, but if it works like Enslaved or Heavenly Sword, it will ruin the game.
Of course 60 fps is what we would all like, but did ANYONE expect that after UE3 was announced as the engine? No UE3 game with visuals of this scale and quality has ever hit 60 fps on a console.
I never expected this to be a proper DMC game and that doesn't bother me. I was never a huge fan of the series myself. In fact, I enjoyed Enslaved more than any previous Devil May Cry title despite the fact that its combat was quite inferior.
It's a shame MT Framework was not available for them to develop with in English. DMC4 was quite a marvel. It looks absolutely beautiful, yet runs at 60 fps while displaying at 1280x720 on both consoles. That's pretty damn amazing, when you look back over this generation.