tried it again, and it is a good bit better now because of it :)

So, now that I can actually see stuff, lets talk level (or rather, screen) design. Make sure that the places to go to the next screen are safe. Otherwise people need to make blind jumps and you get unavoidable deaths that are just not fun. For example what happened here:

I never saw those spikes and I had no reason to think that there would be any there. I just jumped and suddenly I was dead. Didn't even know spikes killed me until I used my grave to go to that screen.

Similarly, there is a row of spikes at the beginning you need to jump over but by doing so you end up briefly in the screen above. This makes it harder than is needed to land your jumps.