Yes, "enjoyable" is a good metric. Because many projects take a lot of energy (years!) before you could commercially profit. For me I would also add "usefulnes

Yes, "enjoyable" is a good metric. Because many projects take a lot of energy (years!) before you could commercially profit. For me I would also add "usefulness" as requirement or like you say it has to be still "worth it" (commercially or learning stuff etc). I had several side projects for years, but various realistic evaluations (competition, market size, production maturity, progress) then led me to the conclusion that I had to stop as they got less useful for me. But stopping them is very tricky when you "enjoy" them :)