Took me like 4 years to beat it when I was a kid.
Although it lacks polish and good balancing, Etrian Odyssey is an original and brilliant dungeon crawler, which made the most of the Nintendo DS.

The game I wasted most hours on

I'm biased but probably the definitive Dragon Ball game until now.

Eroge that aged really poorly, I still kinda enjoyed it though.

My rating is based on the first years of the game, especially since this game no longer exists, unfortunately.

Old Eroge with dungeon crawling mechanics.
It's actually a game from 1993, which, for its age, is pretty impressive.
It's a really long game, so long that the NSFW content becomes secondary.