Simple and interesting gameplay with increasing difficulty already makes a great game, but you went even further by creating "horrorish" environment, thinking about small gameplay details (Like platforms, that are reachable from ground) and even leaving player with option to fight or run (Well, running seems to be the only option past 1000 score, but occasional shooting is still needed.).
All that was achieved with just rectangles (rectangular parallelepipeds to be precise) in the timeframe of one month and I would play this over many AAA titles. Hence it shows the true power of indie.
Overall: I liked it.