My friend summed it up perfectly, he said that Vidal is our own version of Danilo, he's better than most going forward and has pace but when it comes to defending he'e lost, below average...
Vidal's game against Real Madrid actually reminds me of Danilo's against Celta Vigo, Danilo drifting in and acting as a forward and having no sense of positional awarenss. But, in Vidal's case, he sometimes drifted and played on the left and center.
I never thought he's THAT bad defensively, truly a shocker, like I said in the Valvarde thread, playing Vidal in the second leg will be a disaster.
His level is against mid-table clubs and that's pushing it, I might even play Roberto instead of him.