I was the same with this.
I got the 360 Pretty much due to the fact of Halo 3 and a Media Extender for the bedroom.
Finished Halo in about 4 days and kinda left it at that.
Played a little online (Thats nothing great either)

Much prefered assaians creed still playing to this day trying to get 100 Complete all flags etc.

Now have moved onto kingdom of fire and Pro Street, prefer both these to Halo 3 aswell.

Just goes to show what hype can do to a game