Finished game score: 6410. I've used snapshots in a Virtual Machine, without that I only reached level 12. It's too annoyng restart from level 1 and die fast in a new level just to learn how it works. This was common in Spectrum games, but maybe this don't work anymore because we have a lot of other games waiting on the line to be played. The last 2 levels are a lot easier than the previous.
Thanks for the feedback. Based on general feedback, I may be adding a stage select option to the game soon so that it will be possible to start the game from any previously completed stage, which will make it easier to practice later stages. The last two stages were made to be deliberately easier as a kind of reward for beating the more difficult ones.