Best. Game. Ever.
My hardest level is called DeCode
. The hardest part is at 00:40 and it's brutal if you don't have very good timings.
Other pretty difficult levels I've completed include Insomnia
(hardest parts at 00:40 and 00:56), Xmas Challenge
and a flying challenge
One of my next levels will be Windy Landscape
, one of the hardest levels in the game. I have almost 6000 attempts on it and barely 35%. This will be torture.