I'll risk a little derailing, just to say there has been loads of research on gamification and it's impacts on the human brain in the last 20 years. It's still being developed, but it's no longer purely anecdotal, how the vast majority of humans approach gaming (also, given how prevalent video games are, it's pretty easy to get large data samples)...Challenges are absolutely critical to engaging people in life, games, education, etc....There is also the need to feel competent...no one likes a challenge they can't possibly do well at....And people also love competition...Again, many of these are subconscious, meaning that you don't think you like those things, but in reality, you still react to them the same as many people who do...
My only point is, is that in gaming, the challenge and then the ability to meet that challenge first or best, is what draws us into video games. Exactly how much fun one has along the way will of course vary, and the theme, setting, characterization, story line, etc will greatly influence the level of fun the game has...
But many people still play Solitaire on their phones/computer, and get a little dopamine thrill from it, and there is no theme, setting, characterization, or story line...with Spider Solitaire, most people play the 2 suits version, specifically because it's still a challenge, and yet, it's one that most can master...