There are many levels, you get points depending on how much gems are removed. (You do not remove all because one has just only 2 of 4 stars ... but this is what increases the ambition is still to provide with more stars.)
By flying and nondisplaceable parts the game is further expanded.
Fun for many! Hours is guaranteed. There are many levels .. (150? I'm not so accurately counted.)
What I like there is no time pressure!