We're 3DS Ambassadors now, people. Time to...wait until September 1 for the games to roll out.
September 1 is when Nintendo will unleash the first wave of free games, beginning with Virtual Console NES releases. When the program was announced, Nintendo said the NES versions for 3DS Ambassadors would be slightly featured limited, with tweaks coming to the versions that would eventually show up on the eShop for purchase.
3DS Ambassadors get both for free.
Nintendo of Europe has detailed the differences between each version, as well as what we're getting with the Game Boy Advance releases.
On the NES side, there will an in-game manual that explains the controls, with a full manual coming later. There will be "pass the DS" multiplayer initially, with wireless versus play in the updated version. The typical "Restore Point" save functionality, allowing you to save/load at any time, will not be in the initial release, but it will come later. Instead, you'll be limited to suspending play via "VC Suspend."
As for the GBA games, there will be full manuals. Neither "Restore Point" nor "VC Suspend" are included, so you'll have to rely on each title's in-game system mechanisms. If you want to stop playing, make sure to exit the game, as there is no Sleep Mode with GBA releases, so your battery will go poof.
In a future update, you'll be able to transfer all of these games to another system.