It might have ruined it for you, but that's a personal thing and not indicative of either the genre or the majority of fantasy readers. GRRM is one author among many and almost undoubtedly the most popular today due entirely to the televisation of his books. His style is also part of a sub-genre of fantasy (I couldn't say precisely which. Personally I don't like the subdivisions but "Military Fantasy" or "Low Fantasy" or "Political Fantasy" might be each partially accurate) and as such, isn't really impactful on the rest of the genre.
Other people may try to imitate him because of his books popularity but personally I couldn't read the books. I think the characters and events depicted are quite vile and not to my taste. I think it works in a TV show and am looking forward to the new series starting next week, but couldn't get beyond 1/3rd the way thru book 1. His characters are not "morally grey" as many often describe them. They're arseholes across the board. Ambiguity and constant backstabbing/betrayal/changing sides is not that interesting truth be told.
The fact is that nothing established in GoT at any point is ever important. Why? Because at any time, anything can happen. Anyone can die, anyone can change sides, anyone's motives could change without warning. There's no point in establishing anything in such a scenario. No culture, person or nation can be expected to act to their type. This means no genuine world building, no real characterisation. Ask a fan of the WoT books to describe the Aeil to you and they can tell you about their value of water and shade, their skill with spears, their customs of Ji'eh'toh and gai'shain, the Wise Ones, the clans and so on. Ask an Eddings fan about Belgarion's world and they can describe the money-oriented Tolnedrans, the horse culture of the Algars or the vile practices of the Grolim.
Westerosi are all just murderous and ambiguous. The only trait they have is unpredictability. I'll grant that he is still able to pull of some shocking moments, but that's about it. Shocking moments based on unpredictability isn't drama, it's just shocks. It's like comparing Doom 3 horror with Silent Hill 2. "Morally grey" is not being nice one moment and evil the next. "Morally grey" is not simply remaining ambiguous about Varys/Baelish whose motivations are never made clear at any time ever; they just exist and plot but with no reason for why. Since magic is so rare in the world (don't know how it is in the books) it also has no real rules or parameters (eg. we don't know what it can or cannot do, who is able to do what and to what extent, etc).
So to come full circle, no, SoIaF has not "ruined" fantasy. It is a good TV show, evidently incredibly popular series and tho it may well spawn copies and derivatives, the rest of fantasy remains unaltered and unphased, stoic as ever. I'd probably put the most influential fantasy authors as Tolkein, Jordan, McAffrey. For the odd readers who, like the OP won't want to read "less ambiguous" stories inthe future, that's a matter of your personal tastes. I know people who'll only read high fantasy, vampire books, urban/contemporary fantasy and so on so your taste is nothing new. It's a personal preference and if book sales are anything to go on, a preference likely to be well catered for for some time to come.