His reputation was mixed, to say the least.
http://www.arizonasportsfans.com/vb/f7/bucks-fans-opinions-on-brandon-knight-218634.html
There was a substantial contingent of Bucks fans who knew him best who were very skeptical of him and glad to see him gone.
Some on this board dismissed that evidence on the grounds that Suns fans are inherently smarter than Bucks fans, which was a pretty weird argument to make.
To me it's very clear that the Suns took a "glass half-full" approach with Knight and saw only what they wanted to see. The analysis was faulty, and would have been even if the move had turned out okay.
The saving grace is that they were to negotiate a contract extension that isn't a laughable overpayment. Within a couple of years, Knight's contract will look only a little bad, and it shouldn't be that hard to move him.