Been having fun testing it out. MelonDS plays well with older hardware with the JIT complier option selected in software mode. I download Phantom Hourglass today and it’s so charming. I love how you can draw on the map and it’s super casual playing with the stylus.
I’m also enjoying Animal Crossing and popping into people’s towns online and mucking around. Some other villages have given me some goodies like a golden shovel 
Sonic Rush is pretty friggin sweet too. What a neat little handheld.
The ace attorney games are apparently really good on DS, but i never played them
seconding spirit tracks and phantom hourglass
Advance Wars was fun
oh Dragon Quest X or so, I must have played 200 hours of that back in the day
Pokemon heart gold and soul silver were good too
I must have played other things I enjoyed as well but I can’t think of anything else