I think that the fact it can't do colour or really high res powerful games is one of the great things about it.
It's retro and that's cool 
The simplest games are often very popular. Pong is always great, tetris is great (I am thinking of perhaps trying it but it will be a struggle with RAM constraints). Think of something like minecraft. it is highly addictive but a very simple idea. Square blocks!
Mowcius