I'm 37 and had moderate crowding on my lower arch (about 5-6mm). As a result, I have damage to one lower tooth because of the way it strikes the upper tooth. I spoke to 3 orthodontists (I recommend you go to an ortho not a regular dentist!). One said Invisalign was poor choice and he recommended braces. The other two said my case was borderline for what Invisalign could handle and I may need additional treatment with braces. I went with one of the Invisalign orthodontists.
I had 6 attachments glued onto each arch. The treatment called for 16 upper trays and 23 lowers. At tray 16, the dentist filed down between 4 teeth, removing about 1mm of enamel. The filing was painless, albeit nerve wracking. I'm on tray 23 now and my teeth are 90% improved. However, they're not as perfect as I'd like so I will continue until they are, even if it means braces for a couple of months. Invisalign worked for me.
Now for the pitfalls:
1. My lisp NEVER went away. They said it would likely improve after a month but here I am 11 months later and I still speak with a lisp. Mine is caused by the upper tray; if I remove it my speech is normal.
2. Invisalign causes an open bite. I noticed a month into treatment that chewing food took longer, as if my teeth were less effective at crushing food. The ortho said that due to the trays being 1-2mm thick, my jaws have adjusted and as a result, the upper and lower teeth do not come together as tightly as before. This means eating takes a lot longer because you have to chew a lot more!
3. Aggravated my TMJ. I had very mild TMJ before but it's worse now. I don't know if it's caused by wearing the trays or by the fact that before each meal I have to open my mouth wide and reach in to remove the tray. When I open wide, it causes my jaws to lock up, worsening my TMJ.
4. Increase tartar/plaque. I am OCD about brushing and waterpiking after EVERY meal. No cheating at all! You're talking to someone who has not had a cavity since age 10. But I still get plaque inside the trays every morning, which means my teeth have plaque. I also have tartar buildup, which I almost NEVER had before Invisalign. I've come to the conclusion that no matter how diligent you are, the trays by nature simply increase tartar/plaque buildup because they trap bacterial and saliva.