The motion blur effect is really creative.

Entertaining, but sound design could use some work- it gets extremely loud really quickly.

It mostly functions.
I have the same issue of forced full screening, so you can add Safari to the list of affected browsers.
Also, I have issues unlocking medals as well, though oddly enough it's the startup medal that doesn't work- the autoclicker medal unlocked just fine.
Maybe it's because the game starts *before* the Newgrounds permission popup comes up?
Maybe a title screen might help, if you tie the medal to pushing a "start" button, so there's a chance for players to login before the game starts?

It's fun, but I can't complete it due to faulty shape recognition.
I've only successfully gotten it to recognize "Envy" once, and no matter what I do nothing registers as "Pride".
Wrath mostly works, but sometimes I draw it and it registers as something completely diffrent like Lust or Greed.
Confusingly, the game seems to have a strong bias for registering gestures as Gluttony, to the point that not only did I get "Gluttony" far more often than "unrecognized gesture", but a SINGLE DIAGONAL LINE is also seen as gluttony instead of being unrecognized.

Other than that, it's a good game.

It's not bad, but it's very short.
I would also recommend not making the sky and the spikes such a similar color, especially in a lineless style like this, as it makes them very hard to see.

It's great- though a translation of the lyrics would be nice.

This is nice. I like it. ^ ^

(Maybe you could reuse it for an animation.)

Looks like a bit like a Betty Spaghetti.

Look at that, we did it! ^ ^
And we even managed to get a number of stickers that could be evenly placed!
(Two short of a full rectangle, but no one's perfect.)

Art's nice, but the description is not understandable.