People will tell you what they want in the reviews. The hard part is figuring out a way to fix it for a price they are willing to pay. Price wins on Amazon every time, unfortunately, so you have to be prepared to sell for less or equal to the competition while at the same time having a superior product. We sell a product for around $20 when the competitor is priced around $18. Our product is 4.9 out of 5 stars with ~400 reviews while the competitor has significantly more reviews but only around 4.5 stars. It's obvious to customers that they're paying a slight premium for a better product when they purchase from us, so we're able to compete. That being said, there's one direct competitor that sells a 3.8-star product for $12 that outsells us 4:1, showing once again that price wins on Amazon's platform.
If you have a superior product, the rest will take care of itself. The marketplace may change and the market may change, but if you have a great product and you offer amazing customer service you'll be fine.
Of course, I'm glossing over tons of details here, but that's the gist of it. You're welcome to ask questions here or follow up with a PM. I'll be glad to help in any way I can.