I'm not a violinist, but I am a music major, and I thought he was pretty good. I noticed him going low like once in the performance (Chicago), but that happens... seriously, he fixed it and it was all good. I thought I heard a questionable note or two, but I wasn't 100% it wasn't dissonance.
I think generally, there is a difference between classical (classical as in not just classical, but what we consider western european 'classical' music.) and 'pop' music today... If you judge them next to each other, it won't work.
I thought he really added to the performance.