I think that the
Twilight films were horrible ideas for those two actors as far as them being taken seriously by anyone who isn't a twi-teen. But I've seen K-Stew (yes, I'm using it too) in a few other movies and her acting has always been good. Even Rob-Patt is good in some of the other stuff I've seen him in despite my having a strong dislike for his face.
The acting isn't horrible in
Twilight, the script is. Don't blame the actors for a crappy script.
Attack of the Clones has the same problem in my opinion. Lots of good actors (with a few exceptions), terrible script.
Ian McShane? Really?

I'm going to turn into my multi-armed form and yell at your general direction.