Lets jump straight to the chase, the most frequent cause of those damning 1 star reviews is crashes and bugs. You can find 1 star reviews for bad design, useless apps, useless features and so on. But the top reason is bugs and crashes. (Crashes are just really nasty bugs)
Below are some actual examples of 1 star customer reviews:
Update killed it
Needs to be fixed Force closes the second you open it
Just doesn't work right
Just ok: This could be a really good app. However, every time I go to E-offers and tap “load to card” it times out. It does this every time. I also get a lot of “info not available” errors. This app is so very slow. I would like to see a pharmacy option added to get refills. I love your store and I will continue shopping there but come on people, FIX THE APP!!
Don't react emotionally to bad reviews
You’ve spent months of effort and capital building, updating and...