Yeah, that can be the hardest part, not just getting a game from “it works!” to “it’s delightful!” but also recognizing whether it’s there or not when you’re so close to it. I think you’re smart to not move on until you’re pretty confident you’ve got something really engaging. Good luck!
By the way, I haven’t touched if for awhile, but I’m still happy to share my train game prototype if anyone is in the mood to play a fully featured but unbalanced game and give me their thoughts. Let me know and I’ll send you an itch.io key.