Pokémon Ranger: Shadows of Almia. :| They pulled everything challenging out of the Ranger series with this game and, just in case you get bored of it and put it down for a year, they make sure to remind you exactly what direction is north or east or west every time they mention it: "You should head east (→) to ____ Town for this mission." Is the arrow really necessary??
Also really easy were the Yu-Gi-Oh! games they used to have on GB/C. XD; The card systems were so, so broken because they couldn't fit any real card effects or anything on the game and the gameplay itself was only slightly like the actual cardgame. I don't remember details, just that it was so easy to cheat and win.
Pokémon Snap was pretty easy too, but at least it was never so easy that it detracted from the fun. u_u;;