I've owned my '90 Sigma for about seven years or so and I've been extremely happy with the car, save for the high cost of parts (although, maintenance is a rare thing, as most of the parts last a long, long time.) The interior is, by far, roomier than any comparable 4-door I've ever been in. The exterior is distinctive without being gaudy. The engine, with 173,000 miles on it, runs just as good as it did 20,000 miles ago. The only issue I'm having at the moment (besides the need for body repair) is the transmission, which is starting to slip. Past that, this is an absolutely wonderful car. On a side note: the reason parts are so expensive is because it was a limited production car for the US. :)
I bought the car for about 3k when I was 17. I liked the look of it and me and my soon to be wife needed a bigger car and anticipating the birth of twin boys. Car has been awesome, it had great get up and go, comfortable. I bought it with 65,000 on it and it has 260,000 now. 3 kids and 10 years later still going strong - just put new paint job on it. I love how people look at it when they see it - no one knows what it is.
The problem with the Sigma is that it was only made for two years and didn't sell very well, so parts are scarce and expensive. Items that would cost $150 on a Camry or Accord could easily be $400 on the Sigma. My Sigma also had recurring front end problems, each front axle has been replaced twice over the years, and it wasn't cheap. Other than that, the car is extremely well made and reliable, the V6 engine is a marvel, body integrity is superb, and the leather interior is very luxurious. I drove my Sigma for 8 years before trading it in, and was sad to let it go, despite the high maintenance costs.