The Bandai WonderSwan never made it outside of Japan and so it dosen't have many English games, and a lot of them are Anime Licensed and a whole lot of RPGs.
The WonderSwan comes in three versions: the classic, the Color, and the Crystal. Color and Crystal are the same system but Crystal has a better screen and less battery life though all of them run on just one AA.
Classic: 30-40 Hrs
Color: 20 Hrs
Crystal: 12 Hrs
The List
Title
Genre
Description
Box Art
Beatmania
Rhythm
Bistro Recipe
RPG
It's like Pokemon but you make your own monsters, really good spritework and high difficulty.
Blue Wing Blitz
Strategy
Excellent strategy game by Square, the graphical quality is just amazing it looks like a GBA game.
Chocobo no Fushigina Dungeon
RPG / Dungeon Crawler
A port of the Playstation game in nice monochrome 2D, just as good but some prefer this for portability and such.
Dicing Knight Period
RPG / Dungeon Crawler
Final Fantasy 1 / 2 / 4
RPG
Perfect ports/remakes of the SNES/NES games, lots of the sprite work is redone and improved.
Ganso Jajamaru-kun
Platformer
A remix/remake of the NES game with improved controls and monochrome graphics.
Guilty Gear Petit 1 & 2
Fighting
Hataraku Chocobo
Board Game
Judgement Silversword -Rebirth Edition-
Shoot 'em Up
A fast-paced score attack game with heavy focus on aggressive play through eliminating enemies quickly. Your shield cancels bullets and destroys enemies, yielding multipliers, but recharges slowly, requiring a bit of tactical use. Available as a port on the Eschatos 360 release alongside its sequel Cardinal Sins. Somewhat of a rarity in cartridge form as it received a limited reprint, being made by an independent developer on the WonderWitch development kit, though it's easily emulable.
Klonoa: Midnight Museum
Platformer
Makai Toushi SaGa
RPG
Excellent remake of Final Fantasy Legend for the Game Boy. This version jacks up the power to SNES-like levels and is totally worth the $5 bucks or so that your average Wonderswan game costs.
Mr. Driller
Puzzle
Namco Super Wars
Tactical RPG
One Piece: Chopper no Daibouken
RPG
Pocket Fighter
Fighting
The only handheld port of the game, and it's a damn good one too.