There are 15 Levels with eight waves per. It takes about 20 min to finish a level. Different combos of characters affect the tower's effectiveness. Also, different characters yield different products at workshop. Easy to play and experiment. Managing Priests (mana), kill zones and rearranging Towers are key. One glitch... I've replayed the game at Hard and added +3 waves... However, on levels 12-14 the additional levels don't appear.