Just watch the first six seasons, and call it a night after watching Daenerys' fleet sail toward Westeros. Let that be the last image you will have of the series, and pretend the last two seasons don't exist.
Season 6 also sucks
As does season 5.
Really, you're better off watching the first three seasons and leaving it there. They form a fairly complete narrative arc on their own.
First four. Danaerys' arc in season 4 sucks, but season 4 completes the John/Ygritte arc with one of the most awesome episodes of the entire series, it completes the Arya/Hound arc in a very satisfying way, and of course the goings-on at King's Landing in season 4 are probably the best storyline in the entire run of the show. It also has Pedro Pascal's best performance of his career.
Fair, I think season 4 isn't as good as the first three but it's still solid television. Everything after that... not so much.
The heart of the show is Tyrion's shenanigans in King's Landing. Seasons 2/3 are the best because they have the most Tyrion in King's Landing content. Those scenes have the best dialogue, the most intricate plots, the most humor and the best acting, they're some of the best TV ever produced.
Season 4 is the climax of that storyline. After that the show completely falls apart.
