This question has 2 answers. Basically it's yes and no.

For example; If you have a Wii U console with your NNID and have other users on it, you can share everything you download with everyone on your Wii U console. So your brother, sister, etc.

And no. You cannot give you NNID and password to a friend and have them log into your account to download everything you purchased. It is tied to one console (for now) until Nintendo decides to release an update to let you log into a different console.

So simple answer, Yes and No. You can share your games+downloads with all the users the console you downloaded them on. But you cannot gameshare like you can with PS3 meaning you cannot go to your friend's house and log in to download games, etc.