Worst: GTA IV
It wasn't optimised for PC at all, is was a performance disaster, even on a quad-core with 2Gb VRAM. What a disaster.
You know.. I can't really say it was awful, it still outperformed the console versions. And for the time it was the best looking game out there, featuring a well detailed open world and was one of the few games doing full world shadowing. Considering the console performance, the engine itself was just slow.
I think my worst optimised games of all time is 2 recent ones. Planetside 2 and guild wars 2. Guild wars 2 is not real bad but they really needed to pull out all the stops in order to get all its nice candy and effects at playable speeds while maintaining battles that can have close to a hundred players on screen at once. Yet looking at cpu utilisation we can see it isn't using most of the capabilities of a quad core system.
Planetside 2 however takes the turkey. I love the game to death, but its load times suck, flying into bases suck and it isn't unusual for half the squad to say they missed the drop in a galaxy because they all lagged out while their computer loaded the terrain in. And it is the only game I have seen where many if not most players have the game crash when logging out, but even after a years worth of patches and because it just happens when you log out, they never fix it.
Lucky for us, planetside 2 is being fixed up for the PS4 and they are now doing a game wide optimisation pass because they have to make the game preform on what could be classified as a mid-high range pc. When we will see these is anyones guess.
Elcs, is it fare to call it optimised though when even old high end PCs have no frame rate issues on it? I remember playing in the public beta, graphics wernt that complex and the frame rate seemed to agree.