Finding ideas in bad reviews?

Hi all!

I've seen some suggestions for finding new ideas by looking through bad reviews in popular products - has anyone had success with this (mostly in finding a new idea, though building a successful business out of it is an obvious plus)? If so, any tips to share?

In particular:

• do you focus mostly on product differentiators instead of other aspects like support or reliability? (e.g. I seen quite a few bad reviews mostly based on reliability / bad customer service, which doesn't sound like a super strong differentiator given that it's a minority of reviews)
• how do you pick a product category? (e.g. just go for the most popular one?)