For me personally, I just hated using the thing. I guess a lot of that was down to the tablet controller. The things battery drained when it wasn't even being used. I'd come back after not using my WiiU for 2-3 weeks and the controller would be completely dead. Just couldn't be bothered with it. Also had the weakest 1st party library for me. Mario Kart 8 was the only must have.
It just wasn't a well thought out or well executed system.