1 star- simple, can be done easily by new and younger players
2 stars- easy, a little thinking required
3 stars- medim, new players might find it tricky, veteran players should find it ok
4 stars- hard, may take veteran players some time to figure it out
5 stars- all those ridiculously hard levels can get this rating
The idea is so people can have a rough idea of the difficulty before they play the level. Perhaps a newbie is fed up with all the hard levels and wants to find an easy one; or a casual player might want a challenging level. The rating system would allow them to find one they want quickly without having to go through them all and play them to find out.
The other suggestion is to display a % or a progress bar on the main menu for each levelset. e.g. say the player has completed 5 out of 10 levels the progress bar would be half full. This gives players something else to work towards.
What do you think?
