My percentage was once a LOOOOOOOOOOOOOOT higher, before I had my daughter (who's 4 months now).

At least half of them.!

probably somewhere between 50-70% of the games I have. Some games I sold after I finished them, so I don't count them. But I have a pretty decent backlog. Probably between 10-15 unfinished/not started games, if you don't count steam.

Hm... I would say around 70% (Which I think is a pretty good number imo)

There are still a few games in my backlog though.

Around 20%. I'm actually up a lot cause recently i try to finish a game in one weekend when i have time.. Rushed though some games which i then will never touch again..

Around 20%, my backlog increased exponentially over the last few years.

Somewhere around 75-80% for beating the main games. If you are talking 100% completions less than 10% for sure.  I don't care about sidequests or trophies / achievements for 90% of the games I play.  I only focus on those for the rare games that I love and can't put down.

I don't play a lot of games, but those that I do play I always finish... Of course, other than sports games or others that have no clear ending...
I do not however collect trophies, so I do not know how my completions translate there...

I usually beat most games that I buy. I'd say about 80% I've completed if you include all games that I own for consoles and PC.

Aside from Shinobi (PS2), I can't think of an unbeaten game.