I am kind of dissapointed to say this, but Kingdom Hearts II. Kingdom Hearts was interesting due to the large amount of boss fights with varying weaknesses which caused players to think. Well, "think" may be a tad too large, but at least you had to dedicate some thought process into what you were fighting. Kingdom Hearts II, on the other hand, usually just had you swinging your keyblade, mashing X until your hand fell asleep. I plowed through the game in just a few days, much to my dissapointment.
Another game that I found was annoyingly simple was the Dynasty Warriors series, which also went into the whole "Mash Buttons" genre.