I'll give you credit for the "opportunity cost" point. Then again, I'm not sure when I decide to consider that in my "do I continue playing or not" decisions.
For example, I mentioned it elsewhere (possibly in this thread I forgot) but I recently beat scooby doo mystery mayhem on the gamecube. Let me tell you, that game is pretty garbage. There were definitely individual things I liked but the game design and controls felt like hot ass. Not to mention the often confusing level layout.
That all being said, I still beat the game. I could even see my self replaying it. So while I'd give it a horrible review, I definitely had fun and yes me being a scooby doo fanatic likely has something to do with the fun I had but beyond that I still feel like I enjoyed the game.
Could I have been doing something more productive or profitable with my time? Yeah. Did I really care? Nah, I was off the clock and just wanted to play and enjoy something. Before I lose sight of my point, I suppose what I'm saying is if you need to consider "opportunity cost" when you're playing a game, you probably need to stop playing it and do something else instead.