Simple covers that give you an idea about the game without spoiling the game were the best, somebody already posted the Mortal Kombat logo and Skyrim book style logo
Never got to play Dead or Alive 4 as i didn't have the 360, but that cover caught my eye. I knew what it was suggesting back then when i was a kid, but the fact that it got my attention, that was the goal.
Effective box art that tells you what your getting.