I still think that level 6 is the hardest, it took me 9 tryes to finish it in less than 1:15:00, wheres all the other levels I completed with the first try...
Could be a bit more challenging. There are quite a few levels that are over in less than a second, in that time its hard to appreciate the beauty behind the design.
 "Neon Race"){kind=icon}
 "Stellar hunter"){kind=icon}
 "Discover Egypt"){kind=icon}
 "BoomsticK"){kind=icon}