I loved the service and had been with the same stylist for 16 fixes: finding a stylist you can work with long-term is key to success with StitchFix, I think. My problem was a little bit sizing (I'm a s/medium and it was tricky for them to get my sizing right especially in shoulders, bust, and upper arms), a little bit fabric choice (I can't stand items made from that "blouse-y" polyester and can't wear anything that clings to my hips or is bodycon and they kept sending those to me despite asking them not to), and a little bit my age and style preferences. I am well over their target demographic age, and had trouble getting them to not send me items meant for someone 40 years younger than me.
What I'd found worked really, really well was to populate my StitchFix pinterest board (and by all means, create one for yourself and link it to your SF profile!!) with items I found in a polyvore account which they used to create the style cards they send out. This way I was certain that they would send me things that were exactly or closely like items that fit my style, and I knew they had those items in their stock. Unfortunately, they figured out that people were pinning their stock items from that polyvore account and shut it down. After that, I gave them one more Fix, but it stunk and I wrote to plead with them to open the polyvore account again, to no avail. So I quit. It was too expensive an undertaking to give them general guidance on my preferred style and have them send iffy items. I found that most of their brands were also carried by Golden Tote at half the price or less, and I've been happier there.
Good luck and I hope you get a great Fix!