Apple TV works okay as far as it goes, however it has one fundemental failing, the inability to access any kind of network storage natively.
You can use third party apps on an iPad or Mac to stream from a NAS to the Apple TV using AirPlay Mirroring - however that means you can't use them for anything else.
If you have an Android device there's an easy solution, to the point that its probably true to say that Android users get better utility out of the Apple TV unit than Apple's own customers.
Download iMedia Share to your Android phone and/or tablet and fire it up. It will find your NAS and Apple TV and then its just a question of selecting what it you want to watch and choosing the Apple TV as the output device. Once it starts playing you can use your Android for anything else you like - it will even continue to stream whilst the Android device is asleep.