That game is still one of my favorites.
Basicly easy but still sadisticly hard (bit bad controls you know).
I still have not finished it.
I got to the last world but being very young I could not finish the stage.
Luckily I found password that leads to pen-ultimate boss.
That I beat, but the last boss seemed indestructible, and only few years ago I found out how to beat it, just haven't tried it yet.