You can go under the ghost ship level and skip the entire thing. There are blind jumps that at the very least need indicators. Sometimes pipe transitions are checkpoints and other times they're not. There are quite a few sprites whose spawn timing is dependent on the screen scroll. There's no consistency to the look of blocks that kill you.
That said, that's all stuff that could be cleaned up in a 1.1 and I enjoyed a lot of it. Good tough boss fight.