Edit) I don't believe I made this post. I was at work until 30 minutes ago! However, I'll still edit it to make things a bit more clear.
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For your first question, here is a list of the best games - in my opinion - on the Nintendo DS. They will be sorted within their respective genres by how much I recommend them.
Color Key:
RED = US VERSION NOT RECOMMENDED
GREEN = NO WESTERN RELEASE BUT FAN TRANSLATION AVAILABLE
BLUE = NO WESTERN RELEASE AND NO FAN TRANSLATION
LIGHT BLUE = NO WESTERN RELEASE, NO FAN TRANSLATION, AND NO FAN TRANSLATION NEEDED
YELLOW = WAS NOT RELEASED IN US BUT HAS AN OFFICIAL ENGLISH RELEASE
PINK = WAS DISCONTINUED EARLY ON AND MAY BE DIFFICULT TO FIND PHYSICAL COPY
ORANGE = PERIPHERALS NEEDED
BOLD = ONLINE FEATURES
BOLD ITALIC = ONLINE FEATURES DO NOT WORK IN FLASH CARD
NO FORMATTING = RELEASED WORLDWIDE, NO FAN TRANSLATION NEEDED, NO ONLINE FEATURES, WASN'T DISCONTINUED, AND ALL VERSIONS ARE OKAY
This color key only works with approximations, as I am not sure for all of the games listed.
- Survival/Horror
- Nanashi no Game
- Theresia: Dear Emile
- Rhythm/Music
- Jam with the Band
- Meccha! Taiko no Tatsujin DS: 7tsu no Shima no Daibouken
- Taiko no Tatsujin DS: Dororon Yokai Daikessen
- Utacchi
- Rhythm Heaven
- Osu! Tatakae! Ouendan!
- Moero Nekketsu Rhythm Damashii! Osu Tatakae Ouendan 2
- Elite Beat Agents
- Guitar Hero: On Tour
- Taiko no Tatsujin DS: Touch de Dokodon!
- Turn-based RPGs
- The Wizard of Oz: Beyond the Yellow Brick Road
- Chrono Trigger DS
- Dragon Quest IX: Sentinels of the Starry Skies
- Dragon Quest IV: Chapters of the Chosen
- Dragon Quest V: Hand of the Heavenly Bride
- Radiant Historia
- Final Fantasy III DS
- Final Fantasy: The 4 Heroes of Light
- 7th Dragon
- Final Fantasy IV DS
- SaGa 2 - Hihou Densetsu: Goddess of Destiny
- SaGa 3: Shadow or Light
- Strategy/RPG
- Final Fantasy XII: Revenant Wings
- Final Fantasy Tactics A2: Grimoire of the Rift
- Heroes of Mana
- Action/RPG
- Tales of the Tempest
- Tales of Innocence
- Tales of Hearts
- Kingdom Hearts Re: Coded
- Kingdom Hearts: 358/2 Days
- Mario and Luigi: Partners in Time
- Mario and Luigi: Bowser's Inside Story
- The World Ends with You
- Action/Adventure
- James Cameron's Avatar: The Game
- Final Fantasy Crystal Chronicles: Echoes of Time
- Solatorobo: Red the Hunter
- Okamiden
- Shounen Kininden Tsumuji
- The Legend of Zelda: Spirit Tracks
- Final Fantasy Crystal Chronicles: Ring of Fates
- The Legend of Zelda: Phantom Hourglass
- Children of Mana
- Platformer/Metroidvania
- Castlevania: Order of Ecclesia
- Monster Tale
- Castlevania: Portrait of Ruin
- Sonic Colors
- Rayman DS
- Alice in Wonderland
- Puzzle
- Mr. Driller: Drill Spirits
- Ghost Trick: Phantom Detective
- Picross DS
- Picross 3D
- Tetris DS
- Racing
- Mario Kart DS
- Diddy Kong Racing DS
- Misc
- Trauma Center: Under the Knife
- Trauma Center: Under the Knife 2
- WarioWare: Touched!
- Trace Memory
- Final Fantasy: Chocobo Tales
- Animal Crossing: Wild World
- Slide Adventure: Mag Kid
- Jump Ultimate Stars
- Super Scribblenauts
- Hotel Dusk: Room 215
- Last Window: The Secret of Cape West
- Tomodachi Collection
- Love Plus