They work exactly the same as how they work when played on a regular DS or DSi.
Yes, the Nintendo 3DS can play DS games as well as 3DS games in 2D
sorry. DS games can be played on a 3DS in 2D. 3DS games can not be played on a DS at all.
No. The 3DS is region locked, EU games will not work on a US 3DS.
No, 3DS games only work in a 3DS or 3DS XL.
It'd be nice if a next generation console's games worked on older generation consoles, but how would that be possible? The 3DS is a much more powerful console than a DSi, and its games need that extra power to be played - even in 2D mode. Imagine forcing DS games to be programmed to play on the technologically inferior GBA, or GBA games to work on the GBC, or Wii games to work on the GameCube. Doesn't make any sense. 3DS games are programmed with the capabilities of the 3DS in mind, even in 2D mode, there is no way a DSi or DS could play them.
No, 3DS games only work on the 3DS and 3DS XL as well as the 2DS
no
Yes
No, 3DS games will only work in a 3DS.
No, they only work on the 3DS platform. But, you can play DSi and DS games on your 3DS.
Yes, dsi games works on the 3DS also DS games work on the 3DS.
No, the 3DS is region locked.