gta 4 has incredible texture resolution at the high setting and has a lot of adjustable graphical settings, yet its still an appalling port. dirt 2 is a console port with effects tacked on that are way way less impressive than either of the the nvidia settings in mafia 2.
why is just cause 2 a great pc game? and not a dodgy port?
The question here is what makes GTAIV a appalling port and JC2 not one. My conclusion would be the length of time taken to optimize the game for the specific platform. It would appear that in the case of Just Cause 2 a lot of effort was put into making the game perform and look great on all platforms(was it developed seperatly on the different platforms?). GTAIV on the other hand was not.