I have countless games I picked up for less than 5 dollars and only tried for a day.
And a few I never opened.
Like Deus Ex: Invisible War (got it, let a friend borrow it, saw it at his house, took it back, and never bothered trying it for myself.)
And Sudden Strike (1-3 and expansions) is still shrink wrapped.
And Trickstyle, there's one you won't think of. It looked like SSX Tricky on hoverboards, and I never opened it even though it's been several years.
Those are just a few off the top of my head. This doesn't count games I have but never played because we 'store' things in our basement for people, including older computer games that I should really get around to (Planescape Torment, Dungeon Siege one, Freespace one, etc.)
Some of the greatest deals I've gotten -and played- include the Unreal Anthology: 4 unreal games (UT99, UT2K4, Unreal, and Unreal 2) for 5 dollars. Both '99 and 2004 come with the game of the year edition/director's cut extra bullshit including some better maps and mods, etc...
Another one was a box of sequels:
-Dark Reign 2
-Heavy Gear 2
^ All of these combined for 10 dollars, and this was at least 5 years ago when they were almost new.
Another one was Unreal Tournament (when it was newish), and Total Annihilation in a group for 10 dollars...
Fallout 1 and 2 in a little case together for 5 dollars...
Descent 3 and expansion for 5 dollars (same little case thing)
Etc, etc. These are just package deals, I could go on forever. I got max payne and max payne 2 for 2 dollars together...
I'm 19 by the way, these purchases were from when I was 12-17.