Oh man, it’s going to be a bit of a list. Ok, here we go.

Tetris DS - Not Tetris Party. Party hardly has any single player value.

Rayman DS - It is a pretty good port of Rayman 2, you use the stylus as the analog input. It’s kind of tricky at first, but you get used to it pretty quick.

Advance Wars - No introduction needed. Turn-based strategy, sequel to the GBA games. As good as always.

Super Princess Peach - Fun platformer, Peach has several abilities.

Izuna: Legend of the Unemployed Ninja - The story is cheesy, but it’s a fun randomly generated rogue-like

Picross and Picross 3D - Fun and challenging ‘nonogram’ puzzles

Geometry Wars - Space shooter with button or analog controls, earned power-ups

Dungeon Explorer - objectively, not the best action RPG. But I have been playing Dungeon Explorer for the TG16 since like, 1991. So, I can’t help but like it.

Solitaire Overload - So many types of solitaire. My favorite is Spidercell

Jewel Master :Cradle of Egypt - it’s a jewel game. Of the ones I’ve tried on the DS, that’s my favorite.

Mario Kart - Self explanatory.

SimCity DS - It reminds me of the original SimCity, graphics are more similar to SimCity 2000. It just eats my battery, though.

Yoshi Touch & Go - not my favorite, but my wife likes that one

Dementium - I can’t believe the fit an FPS that good on here.

Now, if we want to get into homebrew, I haven’t used a whole lot. Haven’t figured out DLDP yet. But, here’s some that don’t require any extra work that I like:

Worldofsand-0.1 - A falling sand sandbox game

NDS_Shisensho - it’s all in Japanese, I have no idea what any of it says. But it’s a matching game using mahjong tiles

Lameboy - Gameboy emulator

NitroGrafx - Turbografx emulator, but it runs better on the DSi and above

WabbitDS - a TI-83 emulator! It’s a challenge to set it up the legit way, which is to dump the ROM from your actual TI-83. Which I did. But I’m sure there are less legit means to get it going.

DSx86 - DOS emulator! You need this specific open source DOS kernel to get it going, and the folder structure is kind of specific. But it is DOS! On your DS!

I have the hardware, but the games i have right now are

New Super Mario,
Dark Spire

Ill have to try dungeon explorer and Dementium.
Handhelds are fun to have on a steam deck