Season 4. Peak of the show. Closes out the first act of the story by wiping the slate clean in some devastating ways. Takes three seasons of character dynamics and delivers on every single conclusion it offers up. The King's Landing storyline is probably the best storyline in the whole show. It even starts showing signs of having an increased budget, which means we can see every step of the battle at Castle Black instead of jumping over it like we would have done in the first 2/3 seasons. There's one weaker episode ('Breaker of Chains') but it's packed full of everything you'd want from the show at that point in its run.
Season 1. Works brilliantly as an isolated story. It could have been cancelled after Daenerys' dragons were born and your imagination could have filled in the rest. Introduces you to an amazing, immersive world - the likes of which TV had never seen before and arguably hasn't seen since - with some instantly memorable characters who have murky, sinister ethics. It's intriguing, frightening, dangerous TV. 'Baelor' changed TV for the foreseeable future and I'll still never, ever get over how I felt when Daenerys emerged from the ashes of Drogo's funeral pyre. I watched the episode just a few weeks ago, before Christmas, and I still cried - even after all this time.
Season 3. Without the Red Wedding this would probably be level with, or below, season 6, but it does have the Red Wedding. One of the most devastating and numbing episodes of TV I've ever seen (up there with 'Bastogne' in Band of Brothers or the Chernobyl premiere for how utterly battered I felt after it cut to black), and the build-up to it is quite something. Takes a little while to grind through the gears at the start but 'And Now His Watch is Ended' & 'Kissed By Fire' are a tremendous one-two hit. I've also always been a big fan of 'Second Sons', the episode with Tyrion and Sansa's wedding, which is basically a powder keg for 50 minutes that ends with Sam slaying the White Walker.
Season 6. This is "peak Thrones" too, just for different reasons than season 4. This was when it garnered feverish worldwide attention for the first time - when it made its jump from being a popular HBO show to being the biggest show on TV - but still had the fans excited. 'Battle of the Bastards' & 'The Winds of Winter' is probably the best back-to-back the show ever had ('The Winds of Winter' is the show's best episode). And even before then it has Jon's resurrection and "Hold the door!". Has a couple of weak moments ('The Red Woman' is pretty meh; 'No One' sucks imo) but the scale the show was operating on by this point was unlike anything we'd seen on TV before. Not the best season but definitely the most exciting.
Season 5. Unfairly maligned. Has a couple of clunky moments, and it seems they do now regret doing the Dorne plot the way they did (which I think is fine), but this does a really good job of narrowing the focus onto the main characters, instead of adding in loads of directionless subplots (ahem, George). Opens up the second act of the story by declaring its confidence to set its eyes on the endgame. The run of 'Hardhome', 'The Dance of Dragons' & 'Mother's Mercy' is probably the show's most gruesome and bleak three-episode run. It's the fall before the rise. Also crucial for Jon & Daenerys' stories and how things eventually turn out for them both.
Season 2. Great season, just doesn't have that many high-points, which is strange considering every other season is stacked full of them. This does a lot of admin to prepare for life after Ned Stark, and it does a really great job of keeping things ticking over and introducing new characters in this amazing universe. The introduction of magic to the show is something that it struggles with initially but it eventually gets there, and 'Blackwater' remains my second-favourite episode of the whole series. Just a very consistent mini-story overall that rarely reaches unbelievable highs but never drops below a very solid threshold. Also love everything that happens with Theon during this season.
Season 8. Obviously everything happens a bit too quickly, but the ideas on display, and the conclusions it reaches, were too close to what I took out of the show (in terms of its themes & messages) for me to not think it was really brave and bold to do what they did. 'A Knight of the Seven Kingdoms', 'The Long Night' & 'The Bells' have become three of my favourite episodes of TV of all time and I think they more than make up for the exposition-heavy 'Winterfell', the breakneck confusion of 'The Last of the Starks' and the relatively drama-free, box-ticking series finale. Still can't wrap my head around the ambition and scale of 'The Long Night' & 'The Bells'. At its best, GOT changed what television could do, and those two episodes are part of their greatest hits.
Season 7. Still enjoy this season overall. It's driven mostly by us finally getting first-meetings and reunions that we'd waited years for and it mostly delivers on them. Just think you can see the writers really straining to set the board up for the final season. The scale and ambition of the show is still incredible, but Westeros suddenly shrinks in size because things have to happen, characters start acting out of desperation because "there's no time" (as Jon keeps saying), and so you end up with real pacing problems - and whatever happens at Winterfell with Sansa & Littlefinger is the worst thing the show ever did. Still, those first 3/4 episodes (culminating in the battle with Dany & the Lannisters) are great quality and the season finale's subdued tone and slower pace make for great TV.