Basic
Ok well you've much met the basic requirements for a game.
I would suggest taking off the ability to hit the button that would rotate you 180 degrees. Ex: I am moving up and have a train of at least 3, and I press the down button, and I die. Now I understand that yes I did just push a button that would send me over myself. This just adds a frustrating factor to the game, where in every other "Snake" incarnation I have played, the function to commit suicide in this way was not possible.
The animation is pretty basic, but it works for sure. I liked how you made the face change when you die. Maybe add in a little chewing thing when you eat a circle (apple?)
Sound! I endend up playing some music, because the silence got boring. Add a track or two or more that cycle.... maybe make a few buttons at the bottom that let you choose between a few tracks. (grab stuff from this site even if ya want!{if it says thats legal})
Now I know snake is not the most exiting game, so I was not expecting much. Just because the game is not supposed to be riveting, doesn't mean you dont have to try to better it.
Ex: Add a leveling scheme to it; every time you get 10(or whatever number you choose) apples the game resets and your snake moves a little faster.
Or maybe you just go faster ever 10 apples, but keep getting longer too.
This also gives you a way to make the game more exiting - change up the background and/or music when you reach one of those points I mentioned above.
Maybe add some obstacles - rotten food that shrinks you and/or subtracts from your score.
Change up the shape of the level, maybe every 10 food chunks.
Any of these things would make me want to stick around. I found that after about 2 minutes of playing I became bored. I was progressively getting a longer tail every time I played, but there was nothing that held me there, making me want to get that next apple.
A final note, instead of always seeing "you messed up" add a ranking system, based on your score maybe?
Hope that helps, good luck in the future.