"This isn't fun, it should be more fun"
Well then.
My knee-jerk reaction is: "Wait, are we playing the same thing? Am I not getting the story through?" There's a certain level of "this isn't meant to be fun" argument that I know I'd be losing, but it's there. Yet, they're right: if you strip out the story, then it's a series of button presses, right? But what are we left with for games? A series of user inputs; and visual/aural output. What's the fun in that?
So, what is fun?
This may appear like some sort of philosophical bullshit question, like "what is life", but it really isn't. In fact, there's a few established papers/talks that covers how "fun" can be defined. The two that I think I've gravitated to is Marc LeBlanc's 8 Kinds of Fun and Jason VandenBerghe's 4 Types of... (yes, I'm aware of his talk at GDC 2012 on 5 Domains of Play, but I wasn't at GDC, and the slides feel like they need more context). In both cases, they lay out the foundation of what people find as "fun" in games: they're not blueprints on how to make a fun game, but if you analyze a game where someone claims they find fun, you can directly correlate what they find fun onto that list. I highly recommend reading them over if you're interested.
Why I point them out is that in both cases, it's pretty much agreed on that "fun" is not a constant: no two person will ever find the same game fun, and their definition of fun can wildly change depending on their mood, the ideals that they hold and the experience they want to obtain. Someone who would enjoy Heavy Rain for it's storytelling (and finding that fun) may still find LA Noire's story fun, but not it's combat and exploration; Someone who enjoy Peggle's audio visual experience may find Bejeweled's number crunching to be annoying.
These themes and examples are interesting, because it points to that a certain type of "experience" that can define fun isn't necessary true for everyone, and in fact, it would be downright impossible to try to appeal to everyone's sense of fun without possibly alienating someone else.
So, back to my game...
I don't know how other people see it, but really, there's only two levels of enjoyment here: 1)The sense of challenge (in the method of completing the game, and in high score), and 2)A feeling of completion for the story. That's about it. The game and it's subject matter just won't lend itself to someone who wants to feel rewarded and feel good about themselves. There is no happy ending, there is no exploration, there is no competition against someone else. It's you versus the machine: echoing the theme of the game.