Most underrated system

[Leynos]

 SEGA Saturn-Huge and fantastic Japanese library

PCE Engine/TurbografX/CD-Same as Saturn

SEGA Dreamcast-Pioneered a lot we take for granted today and while the US Library was great, yet again Japan library huge and amazing.

PlayStation Vita-Noticing a theme? Japanese library

Neo Geo Pocket/Color- A lot of great gems from Fighting games to puzzle games to a few RPGs and Sonic/Mega Man

WonderSwan Color. In the late 90s portable mainline Final Fantasy games and the last system designed by Gunpei Yokoi.

SEGA Game Gear. Batt life sucked but it had quite a few gems.

All fantastic with huge and great libraries.