I can't speak about the Sigma 9mm specifically, but I've got a Sigma 40VE in .40 S&W and I really like it.
When I bought it, I was actually looking at several different pistols, including both a GLOCK 22 and 23. But, I've owned many S&Ws in my life and I've never had a problem of any kind with any of them, so I decided to give the Sigma a try.
GLOCKS just don't feel right in my hand. I've tried to adjust to the odd feeling of them, but it's just the way it is. However, the Sigma feels like it was custom made for my hand. The quality of the internals, the black polymer frame, and the stainless slide (including the three dot sights) are excellent, and the same can be said of the two mags that came with it as well as the two high caps I received free from the factory after the purchase.
Another important aspect to me about the Sigma is that S&W is again (Thank God) an American-owned company. Some people may think I'm old fashioned for having that attitude, but that's their problem and not mine. I make no apologies for buying American.
Some say that the Sigma is just a ripoff of the GLOCK, but I disagree. I think they have a better design overall, especially in the frame. Others claim that the Sigmas have 'problems' of one kind or another, and that may be true of some of their earlier designs. However, It's been my personal experience that there is more talk than actual evidence to support those claims, especially concerning the later models like the VEs.
To me, the Sigma was an easy choice. Better feel, better design, better quality, better price (by far), good factory support, and to top it off, American made by a company that has long been a favorite of mine. What was the downside? I don't regret buying mine, and I feel pretty sure I'll buy another someday when the right opportunity arises.
These are strictly my opinions, just as are any comments you may hear or read from anyone else. But as far as I'm concerned, I give the Sigma 40VE an A+ rating.