Yeah you need to understand the target market and what they will enjoy, but consumers are relying on you to think of things they will enjoy that they haven't experienced yet. You can't just say the consumers liked the last game so we'll just make something the same. Its the game designers job to think of something new that consumers will like. Its also really hard to think like a consumer once you start learning about how to design and make games anyway. You can't help think about whats behind the gameplay.