The goal of the emoji picker is (presumably) to strike a balance between streamlining the submit-feedback flow and ensuring that the feedback is actually helpful to the restaurant. I chose to use a few emojis and short descriptions to create a mini-review that attempts to capture the metrics on which one might judge a restaurant. This way the user still gets the ease of picking emojis rather than being forced to write an actual review, but the restaurant also learns what exactly they can do better (instead of just receiving an inscrutable frowny face). The final design probably couldn't be called an 'emoji picker' but I assume you're more interested in how I think about product design than my ability to implement a perfect emoji picker.
