The wonderswan was made for Bandai, nuy Gunpei Yokoi, who had left Nintendo after the virtual boy debacle. The best game is named after him, Gunpei is a great puzzle game

Oswan, the Wonderswan emulator

According to Retrogamer, check out
1. Judgement silverswor..Shmup..in tate mode!
2. Gunpey
3. Mr Driller
4. klonda, platformer with interesting switching perspective from horizontla vertical
5. Rhyme Rider - Rhytm Action, Colourful
6. one piece - 2d fighter
7. Ganso - Arcade ninja classic
8. Rainbow Island Putty's party.. Rainbow islands with a female lead.
9. Tane Wo Maku Tori -Guiding falling raindrop arcade puzler
10. Gundam Operation UC - Scrolling Shooter.

and the
Densha de Go version on it sold incredibly well.