S&W's first production of Sigmas were crap... the current production is very well made. Many shooters don't like the Sigma for two reasons.
1. Past Production Problems (Solved since S&W was purchased from the British and made an American owned company again.)
2. Heavy Trigger Pull. Many shooters don't like them.
The current production Sigmas are 100% in my opinion. The trigger pull is a little on the heavy side but that does not bother me. I view the Sigma as a pistol that goes bang every time the trigger is pulled. Not everyone can afford a $2,000 Custom Made Wlison Combat 1911-A1. Some folks can only afford a $250 Sigma.
As I said, the first production models were crap but the current ones are 100% a okay in my book.
And here are some other opinions of them...
http://www.gunblast.com/SWSigma9.htm
http://carnival.saysuncle.com/003084.html