So I just finished The Witcher 3. Loved it.

But funnily enough, everyone(my brother included) have been playing it for 83 hours without even reaching the end.

I finished it in precisely 48 hours 38 minutes.

I finished all the quests except the ones that I couldn't because of bugs(such as the Soldier Statuette quest), completed all but two contracts, reached level 35 and scored 54% of the achievements.

Was it the treasure quests(which I found too boring)? or is it Gwent?

Try to uncover all points of interest(?) and little quests(!) in each area.
They're often offer more than a usual bounty - good view from the scene etc.
I've just arrived on Skellige, 22 lvl and ~70 hours of gameplay. And i see that there is a lot to do here.

Ohhh. Sorry, looks like GOG Galaxy was misleading me.

In the character menu it says a little above 8 days. Which translates to about 192 hours, haha.

But wait, I read online that that counter is possibly bugged.

Any idea which I should be believing?

Believe your wife and/or kids about how long you've been away...

My in game counter registered at over 480 hours at one point. This was just 3 weeks after release. No Way I'd spent so much time in game.

Hm... well, I think both counters are incorrect.
I don't think there's any way to have reached level 35 without completing most of the quests and contracts from what I can infer from other people's stats.

If you run from your shortcut, the Galaxy counter won't register that either. I'm pretty sure there's no way to do most of the sidequests in just 48 hours.

Ah. Thanks. :)