I have to say when I posted this I actually only played the two first levels.
When trying others I was disappointed by the violence, those brutal mines and got frustrated by the difficulty.
If I were the one who designed the game I would have made many levels in the way of the first one with the same difficulty and maybe after that more difficulty ones.
But I'm not a 'hardcore' gamer, and Lemmings for instance was too difficult to me after a certain level, too!

My vote goes for more levels with less difficulty before the harder level!