Did you get your 3DS registered and ready to receive a bunch of old games? Good. Nintendo has detailed the features of the ten NES and Game Boy Advance games that you'll be entitled to.
The first round of NES games will appear on September 1 as "priority delivery" titles, which is a fancy way of saying "unfinished." These games are missing some features that will be available when they're released to the general public, chiefly the ability to save your game by making restore points, the ability to play simultaneous multiplayer, and an electronic manual.
"Priority" versions will include a VC suspend function to at least keep a temporary save point, turn-based multiplayer on a single system, and a basic manual with control details. The games can be upgraded to the full versions once they're available to all.
The Game Boy Advance titles won't feature VC suspension or restore points, ever. However, GBA games can have their regular save features utilized, so it will be just like playing the game IN REAL LIFE! That's our Nintendo, even with something as simple as game emulation, they have to be random and weird about it.