I think your current tileset can be used for at least three levels total. Maybe you can expand it a little bit if you feel it's repeating too much. But adding interesting gameplay mechanics will keep the attention running. I really like your game. And I still advice trying spritefonts. There are many free to use spritefonts. Just run some searches on these forums on how to use spritefonts and they will add alot to your game. You will have a much nicer title screen and much better in-game text. I know it's a hassle and feels like a loss of time when you could do more levels and more monsters instead.
I think your game is coming along nicely and has a solid base to expand upon. Will keep following. Very nicely done.