I don't know that I'd call them harder, but there's a lot more to deal with in Cata dungeons. A lot of running around, switching targets, CC-ing and interrupting and the "cleanse or move out of owie crap" is less forgiving. There were only a few things in Cata that I felt I had to overgear to succeed. In Wrath, I felt I had to overgear just about everything and in quite a few places, no amount of overgearing was helping.

I'd probably go with "more sucktastick". Not hard...hard I can overcome with practice and maybe a little gear. Because of that, I've just canceled all my accounts again.