I've never played Sanitarium, though I own it.
I've never played Darkseed 1&2 and I owned both, now I own only the first one.
I've never played any of the King's Quest games even though I do own Roberta Williams anthology set in mint condition.
I've never played Last Express the full game, even though I've owned it for a couple of years now.
Do I need to continue with the listing?
Then again adventure games I haven't finished yet, but have played: Stilllife, Broken Sword 1, Gabriel Knight 3 and so many more.
There are of course also some adventure games that I've played and would've never wanted to play, if I had known how horrible those were, mainly I'm talking about Escape from Monkey Island.