As something that defies typical genres, "Quintessence" is a little hard to review.
1) From my play, definitely IF more than a "game."
2) The prose can be called "surreal." Odd or unconventional descriptions and metaphors. There's the typical synesthesia type thing (smelling a sound). But even a few moments of play will give an indication of what to expect throughout the whole game.
3) The mood is light. The tone is generally comic, though perhaps occasionally some options that seem slightly more serious arise.
It's unclear if there's some intended meaning or a serious theme is being addressed. I think this game is meant to be an entertaining reading experience; to me, it does not imply the need for intense contemplation or encourage the player to search for deeper meaning (either personal or universal).
As a piece of experimental writing that isn't striving for thematic complexity, I'd say it works. As with much experimental writing, personal taste will largely dictate if one enjoys the author's style. If it was aiming for something more profound, perhaps I purposefully settled on the easier task of reading for pleasure rather than depth.