I bought the Sigma this week. I have not had time to do very thorough testing, but what I have seen so far is very good. Build quality seems to be very high and it gives a very good feel. It also looks very good. This is the only non-L lens I now have and I was initially planning for the 35mm f1.4L, but I read some initial evaluations of the Sigma and decided to give it a try. I have used it on 1DX and 5DIII and balance and operational use is very good. Resolution, vignetting and CA are all first class. AF is not the fastest I have seen, but for the kind of use most people would use this lens for, I´d say it´s good. I´ll bring it to an event tomorrow, and will probably put it through some more challenging situations then.