Yahtzee nailed it on the head with the x-rays. I don't mind gore in video games, and they were fine the first time you watched them, but they got so boring so quickly. The reason fatalities worked in previous games was because you only saw them at the end of the fight, and then only if you knew the right button combo - and most fighters had multiple ones to choose from.
Being able to do the x-ray slow motion moves mid-fight meant that you got bored of watching it after about 3 fights with the same character. Slow motion gore is for after the fight, not to suddenly stop me playing every 10 seconds to make me watch something I've seen 20 times already.