Nintendo Land was great for the asymmetrical multiplayer. Four players co-op on the big screen versus a fifth player on the GamePad. It's not impossible to do in other ways, but I haven't seen it done.

I think shared/split screen on the TV adds an additional social element to it. Otherwise it's just all of us playing on their phones/Switch.

It was mostly used as a secondary, supporting display: - Zelda Windwaker HD - Deus Ex: Human Revolution - Assassin Creed Black Flag

While it wasn't necessary it freed up screen space for the main diaplay while also allowing you to play only on the gamepad.

Mario Maker used the touchscreen effectively. You could seamlessly go back and forth between editing your level on the touchscreen and testing it on your TV. I also liked the touchscreen effects in Super Mario 3D World and regret their (effective) absence in the Switch port.

Wonderful 101 does it beautifully, entire game was designed to use it in many different ways.

The best overall use is the Nintendo DS emulator. Unfortunately only few games are available for purchase but with a bit of hacking the compatibility is great.

ZombiU also used it well and the mass effect port let you use it to issue commands to your squad mates.

Yes, really innovative use of the gamepad for ZombiU gave the game a properly scary aspect when checking in bags and boxes, and nervously looking up at the screen as you're doing it.

One of the most unique multiplayer experiences I have ever played

In Tokyo Mirage Session you get text messages from the characters on the second screen so it's like you are glancing at your cell phone as you play. This worked very poorly when they ported it to Switch and you had to go into a menu when a party member texts you.

I felt like later in the Wii U's life, they were pushing it more as being for off-TV play, and that meant that that kind of stuff would have to be implemented anyway— Wind Waker HD certainly had the dual approach, where the default was to play on the TV with inventory on the gamepad, but if you played in off-TV mode, then the inventory was a pause menu popup. That extra development work to support both was probably invisible to most users who only ever played on-TV.

That combined with the increasing inevitability that everything was going to be ported to a later, single-screen system anyway, and it's not hard to see why titles like Donkey Kong Tropical Freeze and Zelda BOTW didn't use the secondary screen at all.

It's not just games that are played in off-TV mode, any game that supports the Wii U Pro controller needs to have a single screen option.

Batman: Arkham City. You could use it to tune your radio, hack stuff, remote control gadgets, probably some more stuff I'm forgetting.

Splatoon made me sad that you couldn't do 2-player co-op online with the gamepad and TV. That felt like a big miss.

I used it a lot for planning and multitasking in Pikmin 3, it felt like a really organic addition to the gameplay there.