The way it integrates with other applications and its ability to create different formulas depending on user input (cell value) is amazing! I especially like how easy it is to integrate into your current application workflow if you're already using any formulae or functions that are similar to those in GSheet itself.
Maybe have another option available where users can choose between a Google Sheet-like interface vs. an actual spreadsheet instead of having them pick one when creating their sheet? Not much dislikes but I do wish there was some options/features within each page which allowed me to make my sheets easier to use. If you want something you know will work great even just by looking at the examples then this is definitely worth trying out! We are currently solving problems around data collection from our clients so all of us being able to communicate very quickly without needing.