I agree, finishing the game for me feels better, even if it doesn't live up to your expectations.
I personally come up with a couple themes (around 7 this time) in the first hour and then stick to one of them, then, I start coding the game, play test it and add things that I find necessary right now, after around 24–36 hours I stop adding new features and focus on polishing (sprites, sound, music, animations, tutorials, etc.)
So far it worked very well for me.