Yeah, levels need some balancing in general, specially the last one, but I'm impressed you managed to beat everything! I'm glad you like the story too!
Sound Effects are literally the next step for the game in my spreadsheet!
What's your screen resolution? If you could send me a screenshot of how the boss appears to you that would be of great help! But it might be something about the art itself as that is still placeholder.
Yeah, the speed upgrades are a total tradeover. If you go too fast it might become too difficult, but you can always take points out of the min/max speed bars and put them elsewhere if you feel you went too far with it.
I left the option to go really fast as I think maybe there's some people out there that have enough reflex to get used to it, but I think I need to make some adjustments to vertical speed so that the player rises and falls faster as well or in some speeds you have no chance to dodge at all.
Thanks for the feedback!