the first book is a fucking slow borefest that drags and drags, but it gets a lot better in book 2. the first season follows the first book well enough, and doesnt really start diverging until book 3 iirc so you could try starting there, go for audiobook maybe?
the absence of lady stoneheart, aegon, archmaester marwyn, and other significant characters, the still-undetermined fates of stannis and rickon, whatever tf our faceless bro syrio forel/jaqen h'ghar/the alchemist was doing in westeros (probably there to kill marwyn, who leaves oldtown for meereen, to meet dani, right about then), the absence of azor ahai's sword lightbringer and other unresolved things related to the prince that was promised and [their] song of ice and fire (series title drop), and so forth make for a lot of differences that could make the endings very different, before even getting to the "oh that's too out there to fly with the audience" kinda thing that generally prevents tv shows from diverging too much from "what's working/successful". it'll be worth finding out how different they end up being in 10-20 years when the last 2 (?) books are finally out lol