I wore braces as an adult as recently as 2000. Only a few years after having them removed, my teeth settled back into their crooked state. I postponed correcting them until this year, when I decided to give Invisalign a try. One lateral tooth was moving in front of a front tooth, and I just couldn't live with the look and discomfort.
My case would be considered mild by most standards. Only 15 aligners were ordered, 30 total weeks of treatment.
I've completed all 15 aligners and am disappointed with the results, and with the continuing treatment. The orthodontist hasn't done a refinement, the term for taking new impressions and ordering new aligners. Instead, he has adjusted the last aligner 3 times, several weeks apart, to very little effect. On my next appointment, 16 weeks will have passed from what should have been the end of the treatment. It's possible the size and shape of my teeth are such that they can't come out perfectly straight, though I do believe they should look better than they do. There's a still some rotation on the two upper laterals.
If you're considering Invisalign over traditional braces, Invisalign does have an appearance advantage. Be aware, though, that Invisalign isn't "invisible" like the models with perfect teeth in the ads. The orthodontist will put small attachments, called buttons, to give the aligners something to grab. The aligners have small bumps that line up with the buttons. There are 6 on my front 6 teeth, The overall effect is a bad smile, I look like I have something on my teeth,which I do.
I shopped price, because the treatment is expensive, with a wide range of quoted costs, generally $4,000 - 6,000.
I would recommend Invisalign, in spite of my personal dissatisfaction, over wire braces, having worn both.