Thank you so much!! It feels really nice to hear this :) The last level is indeed not winnable. The player should actually not even be able to start it, but due to a bug its possible.
I was considering to develop this game further (more levels, plants, monster & polish) and put it on steam, but got somewhat discouraged due to the amount of work that needs to be done to make it a success.
Your comment might have just given me the motivation to continue :)