Sadistically hard, like someone forces you to play SFDX level 4 without any warm up! Just try to rotate the small triangle through the partial hexagons closing in towards the centre. I like the way you can restart the game in milliseconds after you lose. I (sortof) like the music (which is actually one tune that starts at random points each time). I like the way the vectors bounce with the drum beat. I also like the synchronised palette changes. I like when I get to navigate out of a tough loop. I like the game's concept. I like Terry's games.
Now go and get slaughtered :)
P.S. Terry, has started a blog about indie games, and so far he's been posting some pretty awesome stuff! I might borrow some of his picks in the future, but in any case, have a look at it, it's worth it :)