Best: You won't believe the money I've saved though GOG.

Worst: Probably the 20 dollar, Android 4.2 cellphone that we got just to have smartphones.

On site: Windforge. That game is deader than Christmas ham that burned down. Even Retro City Rampage with its various odd bugs and general incompatibility with my controller is overall better. (And there's a small chance the game will update, unlike Windforge.)

Best: Chaser (boxed version), loved the style and feel of it to death.

Worst: Breed, I can barely remember the game, but all I remember was that it was awful and I hated every second of it.

Best: Command & Conquer Red Alert Collection (The one with the original C&C + Expansion and Red Alert and Expansions)
I recall being really psyched to find it in the used bin and was not disappointed

Worst: Anything I bought and didn't really play much. But that's why you are trawling the bargain bin, isn't it...

Best: Neverwinter Nights
Bought it for $5 in 2003, then I spent thousands of hours in the game. For several years, I didn't buy any other game as this was all I played. I must say I got my money's worth.

Worst: XCar: Experimental Racing
I can't remember why I stopped playing it, but I just lost interest soon after installing and trying it out.

Best:
Race-Pro ... a 2009 exclusive for the Xbox 360, a collection of Simbin's PC racing sims ported to console.
Not surprisingly its the best sim racing game on console, apart from Project Cars and the upcoming Assetto Corsa and Dirt Rally games, which are all ported from the PC. There's a pattern here.
Not that I don't like Forza and Gran Turismo, quite the opposite, but if you want a sim experience the PC sims are king.

Worst:
Skyrim .. . again on the Xbox 360, I refused to buy it on Steam and found a cheap console copy.
The game was as boring as I expected and I resold it a few weeks later.

Frankly, back in the retail times, 99% of my PC or PS/PS2 game purchases were from "bargain bins", if that means either heavily discounted or second-hand.

It is easier for me to name the retail games I've bought for full price, than those I didn't. Like:

Wing Commander + expansion pack(s)
Wing Commander 2 + expansion pack(s)
Wing Commander 3
Red Baron
Falcon 3,0
Final Fantasy 7 (PC)
Final Fantasy 8 (PC)
The Dark Eye

Maybe there are more, but most purchases were indeed discounted/second hand.

Best: The Sims Complete Collection
Do I need to say anything? It's the original Sims with all the XPaks.

Worst: Soldier of Fortune:Payback
I love the original 2 games especially the second one but this travesty is just ...atrocious.

Hmm, best find? Guess that must be Fragile Allegiance for the equivalent of 40c in 1999 or around then, 2nd best was Homeworld for €2 some five years ago. Worst was Massive Assault (€3 I think it cost) as I did not get into it at all even it looks like a good game.