I think a lot of gamers are suffering from a lack of understanding of the true feeling of satisfaction after a true challenge is overcome, also known as "Supreme Sergeant Master of Sergeants!" Syndrome.
See * here * for details.
Sounds like you just burned yourself out man. You should be happy that you got that much enjoyment out of one game and you definitely got your monies worth.
I played this game for 2 months almost daily, took a month off to play kz 3, and now I'm back to DS. I've got about 400 hours in on this game and I still can't get enough.