The 2DS is a sense to the 3D capability facilitated more affordable version of the 3DS. It has also been primarily the younger children in mind and simplifies the product for this. The device is not foldable and therefore more robust. The folding mechanism is worn out very quickly by children and the 3D which many anyway off and is not the best for children's eyes, does not need to be pay full price here.
Otherwise, you can order all the games from the 3DS to play and make use of all other functions.
The included game is a typical Mario 2D jump and run and has given me until now a lot of fun. Also good, I find that accompanies a power supply here. The only downside is the mono speaker, which does not fall so much weight.