It seems that there is no complete list yet and you don't get 20 games right away. An article on kotaku dated July 28th basically says that on Sept 1st you can get 10 games. That list will be NES games and will include Super Mario Bros., Donkey Kong Jr., Balloon Fight, Ice Climber and The Legend of Zelda. Then sometime later in 2011 there will be the list of the Game Boy Advance games and you can select 10 more games. Such games included would be Yoshi’s Island: Super Mario Advance 3, Mario Kart: Super Circuit, Metroid Fusion, WarioWare Inc.: Minigame Mania and Mario vs. Donkey Kong.
I dunno...I'm a 38 year old retro gamer and I legitly have all of the Nintendo games listed here and it's not a big deal for me to be to rebuy them even for free on a new system. They would have to contain new updates as I probably won't play them as I already played these to death over my 30 years of gaming. I know I'll get a 3DS someday, but that day will be when the new Phoenix Wright: Ace Attorney, Paper Mario or Luigi's Mansion 2 comes out. From what I understand those games are still ages away and my 3DS would simply sit and collect dust until then.
What's sad is that when I tested the 3DS demo machine out at Walmart, I discovered that I cannot use the 3D feature on this. I have a lazy left eye and it's incredibly hard for me to focus for very long to see the 3D. In fact I often have to close my lazy eye just to read books, which is quite embarrassing out in public. So I need to put it to the 2D mode and when I do that, it feels like just another DS to me and I was so dissappointed. But if the games came out that I wanted, I would have gladly paid $250 for it as I'm just that impulsive to play my top fav Nintendo games.