I just beat this game in normal mode and I got pretty into the simple pouring mechanics. Trying to the ratios just right gets pretty tricky, especially if a customer asks for a complex mix. It can get pretty difficult to eyeball a drink needing, say, 10% chocolate, then 30% milk, 20% coffee, etc.
One part I really struggled with early on is the lack of immediate clarity on an order. Customers keep asking for generic things like "just coffee", or "just tea", or "just milk", but the visual indicator for what they want includes many more ingredients. Not only that, but there's no visual cue at all for when they ask for toppings like whipped cream or caramel sauce, you only get that info by hovering over the icon. It should be possible for the player to tell at a glance what the customer wants by reading what's immediately on screen. I messed up a number of drinks early on because I forgot something like ice, all because there's no visual cue to this unlike the rest of the drink
Speaking of toppings, there's one small clerical error with one topping: The coca powder. The tool tip when you hover over the drink icon calls it "chocolate" when there's already a "chocolate drink", so you could end up with a customer ordering a "100% chocolate w/chocolate" rather than a "100% chocolate w/coca powder".
Lastly, could you add the option to suspend a game in progress? I was expecting to play just for a few minutes, and while I did stick it out, if I played again, I'd much rather do it in short bursts over a few days rather than in one sitting.