I'll go with Twilight Princess. The boss fights in that game were a joke, especially the battle against Zant, quite literally too. All that build up, you would expect him to be some epic warrior. Nope, most disappointing boss fight ever. It was like fighting a drunk clown.
The puzzles were also fairly simple. There were some that required
some thinking, but that isn't saying all that much. The combat was fairly easy too. And there wasn't really any challenging mini games or long side quests to get an epic item/reward.
The only thing going for that game was the beautiful environment, the design of characters and the bosses, and the addition to the Twilight Realm. Pretty epic story line too, but Nintendo made the game way to easy.