I have this a lot with jRPGs and so many older style wRPGs. I put anywhere between 15-40 hours into the following:
Grandia 1 & 2, Baldur's Gate, StarOcean 3, Xenoblade Chronicles and Pillars of Eternity.
Still plan on going back to the PC games at some point. I don't think I have access to the jRPGs anymore so they're a lost cause.
There are plenty of other games I've started but haven't played enough to include in the list but enough to feel "unfinished" like Doom, Wolfenstein 2, Metro: Last Light and Fallout: New Vegas.