If there isn't good vs evil or black and white characterizations in GoT or ASOI&F, there surely is a very, very strong contrast between the likes of Oberyn and the Mountain. And for that matter the ethics and morals of the Starks and Lannisters. The Mountain has pretty much been established as a complete psycho out to rape, pillage, and murder to his content at the bidding of Tywin, and largely himself since he has no physical rival.
And while Oberyn is no saint, he has a lot more favorable character traits than Gregor. He's out to avenge his sister largely, and her children by extension, for being guilty of only being Targaryen. And he believes that Tywin orchestrated her fate, which isn't a stretch since Cersei got snubbed in favor of Oberyn's sister in been married to the throne. And if I had to distill it, Oberyn died of carelessness. He was arrogant, but he had reason to be, he put the Mountain down in a dominant fashion. While he could've been more prudent since the contest was pretty much won by him at that point, he wanted what he didn't have, which was a confession, and he got it at the cost of his life.
I recently watched a portion of season 1 again and it's not hard to see why fans think this paradigm of Black vs White. In the first book/season we're largely introduced to the Stark family that gets it's family head chopped off and later decimated, largely to the benefit of the Lannisters who have gained nearly all their ground on manipulation, which isn't an honor bound family's strong suit. Just personally speaking I'd rather be an ally of the Starks since I can take them for their word, or at least hold them to their honor, than I could any of the Lannisters. Readers/viewers are also strongly misled from the beginning that the Lannisters are behind the death of Jon Arryn and seek to kill the King and control Westeros in a Windfall. All the while incestously guaranteeing their continued inheritance for some time to come. Add in Jamie's disregard for the life of a child to hide his affair and I think it sets up the Lannisters as a pretty morally bankrupt family. Tyrion, the most empathetic and sympathetic of his group, ignorant but suspicious of details surrounding the events in season/book 1 is held in contempt by his own family, except for Jamie.
So far we've seen the Starks get cut down by the schemes of Littlefinger, Cersei, and Tywin. The Lannisters have pretty much won the Game of Thrones so far. Even with Joffrey dead (which is probably to their benefit) a thoroughbred Lannister sits on the throne at the counsel of the grand chess master Tywin. When it seemed like Tyrion was saved and Obreyn triumphed to finally vanquish one party who greatly wronged him and many others, he was killed savagely with grave consequences.
So as a viewer it's been pretty much every major victory in Westeros falling to the Lannisters. Hell Tywin has even driven a wedge between Danerys and her highest counsel. And then the new champion for the underdogs/wronged and rookie of the season has victory within his grasp but gets brutally killed in the end satisfying the reigning Westeros illuminati. There's a reason why GRR Martin is likened to a troll.
I'm reading a lot further into the future of the overall plot. I'm also pretty sure the White Walkers are pretty much a soulless, and evil force by any living creature's standard, for extinguishing/assimilating life to their/its will. & It seems as though Danerys and her dragons will be among the forces of fire who come to save Westeros from its most wicked Winter yet, while the strife of the major houses will put a big welcome mat out from the common folk for her arrival/save.
But people are right in saying there isn't a one-dimensional, binary good and evil figure (so far) in the series, and things aren't always as they seem (Gregor may be mentally ill for any number of causes). It's a twisted plot with conflicted characters and entertaining as hell. I look forward to whats to come even though most of the people I've invested in got snuffed out in some way or another.