Framerate. As long as it's a locked 30fps I'm fine. If it's 60fps that's better. Varying framerate that struggles to reach 30 is a problem, especially if it makes sharp drops then back to something more stable since it makes it extremely noticeable.
I recently purchased Ninja Gaiden Sigma 2 Plus and the game is unplayable because of framerate issues. It drops once or twice per stage, but then on stage nine it's lagging almost the entire stage. Not fun at all.
The game has been out seven months without a patch either so that also tells you the company doesn't care about its fanbase in the least, so in turn I'll do my best to support them as little as possible. There's no way I can't support them a little though since there are games I want from them still(Dead or Alive 5 Ultimate, Ninja Gaiden 3 Razor's Edge, Romance of the Three Kingdoms 12, Atelier Ayesha) but if I can purchase used in mint condition I will, or purchase the games I'm interested in new, but at the lowest cost possible.