I traded my 09 STI in on the BRZ and have not had any regrets. I never AutoX or tracked the STi and used it as a 90 mile/day DD. So with that, I never really utilized the STI's features to fully enjoy them. If I did AutoX or track the STI regualarly, I might have a different opinion. That all said, I think the BRZ is just such an enjoyable driving experience.
My one knock would be the lack of acceleration "feel", but all things can be improved.