I just bought a new copy of Super Smash Bros. Brawl and tried to play it in my Wii U. Most things work fine. I can play the classic modes and brawl mode. The museum, where you are able to play old games doesn't work for almost all the games. Super Mario Bros 1 for the NES works fine, but every other game just exits to the Wii menu without any error message.
More annoyingly, whenever I try to play Subspace Emissary mode with 2 players, it gives me a disc read error screen and I have to unplug the Wii U entirely to get it to work again. Strangely, if I start it 1 player, and then make the second player join afterwards, it works fine, but if I start with 2 players, it crashes.
This isn't the biggest problem in the world, but I wanted to report it. The disc is flawless, and the Wii U is fairly new, and I haven't had any other disc reading problems with it with other games.