Well, I haven't seen much of the show aside from clips but did read a lot of it twenty years ago when he started the series so I guess we're inverted there. ASoIaF was well positioned in time, it came out right when the Internet was starting its major growth phase and fandoms were booming, but before internet publishing started up and it would have had more competition.
On a technical level they were okay-ish but he was mostly notorious for just much explicit sex and extremely random violence his stories had, at a time when most fantasy was relatively kid-friendly. Books like DnD's Drizzt series, the Heralds of Valdemar, and other relatively fluffy stuff with happy endings were prevalent, to the extent that in The Pagemaster Fantasy says her worlds all have happy endings*.
This reduced the quality of his writing down a stage from good to merely okay-ish because it futzed with the flow and rising tension of the story, he'd spend 50 pages building a character only for them to get stabbed by some rando. I recall a meme back in the day that was basically the cover of the first book and the title replaced with "Everybody you cared about in the last chapter dies in the next chapter."
*It's a movie where several main characters are the personifications of literary genres, the MC goes on a journey with Fantasy, Horror, and Adventure.