You'd be surprised there are alot of adults that like to play on their Nintendo DS systems!  The range from 20 to 66 years of age!  (If you are over 65, let me know! I'll be glad to change the age range!) I am an adult myself and my kids' friends have told them that they think I'm crazy because their "mother" plays on the Nintendo DS.  They all seem surprised whenever they see me playing on it like as if it's only for children.  I've seen kids play on it in public but I haven't yet seen an adult using it.  Waiting rooms are great for using them to pass the time!!

I've gathered some information on what games adults like to play.  Some prefer puzzles whereas others prefer RPG type games where there is a storyline into it.

The games I've gathered that adults like are as follows:

Picross

NY Times Crossword Puzzles

Tetris DS

Wordmaster

My Word Coach

Spelling Challenge

7 Wonders of the Ancient World

Clubhouse Games (big hit!)

Advance Wars

Brain Academy/Brain Age/Brain Age 2

Cooking Mama

For those who love a good mystery, there are the Phoenix Wright: Ace Attorney games, Touch Detective, Hotel Dusk: Room 215, Professor Layton and the Curious Village

New Super Mario Bros

Castlevania: Dawn of Sorrow, or Final Fantasy III if you like RPGs and Legend of Zelda

Puzzle Quest

Meteos (the non-Disney version), Final Fantasy III, Metroid Prime: Hunters, Metroid Prime: Pinball

If you like puzzles: Planet Puzzle League, Tetris Worlds, Magnetica, Nervous Brickdown, Konductra, Polarium, Space Invaders, Arkanoid, Snood On Vacation, Brain Challenge, Zoo Keeper, Word Jong, 7 Wonders of the Ancient World, Professor Layton and the Curious Village, Arkanoid DS (July 2008)

And if you enjoy playing music, Guitar Hero and Jam Sessions surprised me in its versatility and easy to use!

I usually check out games at gamespot. They show screenshots and reviews on each games.  I especially love the screenshots so I can see what the game looks like, whether it's my type or not.  Helps alot!  Gamespot also tells you what new games are coming up in the future. 

I have My Word Coach game for the DS.  My Word Coach, developed in collaboration with linguists, helps players improve their verbal communication and vocabulary in a fun way. Practice need never get boring with six different exercises to choose between. Players can input missing letters from words, spell out the answers to various definitions, choose which word matches a particular definition, form specific words with Scrabble-like tiles, and more. Three levels of difficulty are available, and the game includes a built-in dictionary of over 17,000 words. Two of the games can be played multiplayer over wireless and the data of three different players can be saved. ESRB Rated E for Everyone.  The game is great!  I am learning many many new words! 

As one adult gamer said it very well:  "Don't be shy, pull your DS Lite out anywhere, and ignore the folks who grew up too fast, and will die too young."