The main problem i see is not Nintendos 1st Party its the total lack of 3rd Party.
Even on the Gamecube 3rd Party games were present and sold quite decently.
Actually the 1st /2nd Party is very good. Hell even Zombi U and Rayman/Deus Ex are good efforts but a lot of people are blinded by Playstation/Xbox now a days. Better graphics and no quality seems to be ok.. Just look how much of a mess AC Unity is and the lack of 1st Party Xbox/PS4 games...
The graphics on the Wii U are still better than the HD twins and i think for example Deus Ex/Rayman Legends are the ULTIMATE Versions!
What can Nintendo do?
1. more Advertising
2. TALK to 3d Parties get them back even if it costs a bit. no FIFA/AC and COD is killing the wii U no joke!
3. More games i think Nintendo are doing more collaborations.
4 This may be contriversial but get stuff like Turok/shadowman back ... How popular were games like Turok/Shadowman on the N64... Wernt a lot of Retro ex Turok devs ?
5. More Western Studios... At the moment most of the few games are Eastern centric... In the N64 days we had Rare maybe form a few new studios in the UK/US?