The deadline for enrollment in the 3DS Ambassador program has passed, and now we're receiving more details on the features included in the crop of free games. The free NES games hitting on September 1 will be barebones versions of the originals, with fancy new features added later when the games officially go on sale.
Official Nintendo Magazine reports that the NES titles delivered on September 1 will be "priority delivery" titles, featuring only a basic manual with controls, and the Virtual Console Suspend function found on the Wii. It also promises "alternating" multiplayer for supporting games, a la taking turns in Super Mario Bros, but that's part of the game itself and not an added feature.
Sometime later, the games will be available in the eShop for purchase with new features. At this point, anyone can buy them, but Ambassadors can download the updated versions for free. They will include a full game manual, simultaneous multiplayer on multiple systems, and a Restore Point function like the one found in Game Boy Virtual Console games on the 3DS. This makes sense of why Nintendo promised an update to add multiplayer support.
The Game Boy Advance games aren't quite as feature-rich. They sport a full electronic manual, but no VC Suspend or Restore Point function, and no Sleep Mode when you close the 3DS. You'll just have to save your progress in-game, as you would playing a GBA game on a normal DS.
Nintendo is also planning a firmware update that will allow you to transfer the NES and GBA games to a different 3DS system, just in case that becomes necessary.
The NES games include Super Mario Bros, Donkey Kong Jr, Balloon Fight, Ice Climber, and The Legend of Zelda, with five more games yet to be revealed. The GBA titles include Yoshi's Island: Super Mario Advance 3, Mario Kart: Super Circuit, Metroid Fusion, WarioWare Inc: Mega Microgame$, and Mario vs. Donkey Kong, also with five more games to be revealed. We've seen an unconfirmed leak that Super Mario Advance 4: Super Mario Bros 3 and Kirby & the Amazing Mirror will be among the remaining games.