If you've got a DS or 3DS, you can buy the fucking great Nine Hours Nine Persons Nine Doors, or 999: http://www.gamerankings.com/ds/961351-nine-hours-nine-persons-nine-doors/articles.html
It's not an eroge and not really light-hearted, but if everyone can ignore your request so can I. Anyway, I don't want to spoil anything, but the great thing about it is that it becomes a fantastic physics/philosophy mindfuck firework in the true ending, but it sets up all the material so well and clear the story never 'loses' you.