As for me, I'm finished with my season 3 rewatch, I'm watching a season every other week.
Some "now that I know it" considerations,
obviously TROOPER AND ANYONE ELSE WHO HASN'T SEEN SEASON 3 AND FORWARD QUIT READING.
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- Totally forgot that Qyburn's first appearance was among the wounded survivors of Harrenhall.
- Poor, naive, afraid Sansa: in blurting out to Olenna (all hail Olenna) and Margaery that Joffrey was a major asshole, he set the first step of her revenge, with Olenna deciding Joffrey had to be taken out. You helped avenge your father, Sansa, and you didn't even know it back then!
- Some misdirection about Ramsay's identity: Robb received news that "when the bastard of Bolton arrived at Winterfell, everyone was gone and the place was in ruins". D'uh. He's the one who caused all of that in the first place. Also, a clever hidden reveal when Ramsay pretends to free Theon, and then kills one by one his pursuers: the last one before dying says in hateful contempt "you little bastard", it was not just an insult, but a proper definition.
- Classic moment: Jaimie Lannister getting his hand chopped off, and then the moshpit starts with the punk version of The Bear and the Maiden Fair
- Another classic moment: Daenerys going all Dracarys in Astapor, kicking all kind of possible asses. I guess we all agree this is one of the best "HOLY FUCKING SHIT THAT WAS AWESOME" moments of the series!
- Edmund Tally is one of the worst idiots of the show. He first appears failing to hit his uncle's funeral ship with flaming arrows (which the Blackfish manages to do at the first try without even looking if he had actually shot right, he knew he did - badass), and then does a major screwup conquering a mill the Mountain was holding, which results in:
1) The Mountain not being captured and killed, which would have left Cersei without an unbeatable champion, and Oberyn Martell therefore surviving;
2) 200 men lost, adding to the discontent and sense of not being able to make it to Robb's army;
3) The capture of the Lannister boys that got killed in retalation, prompting Robb to execute the old Karstark (well, his decision, but still...) and losing all of the Karstark bannermen.
WHAT A DICK. He almost single-handedly lost the war for Robb with a single reckless attack. And in turn he both got laid and survived at the Red Wedding.
- Speaking of the Red Wedding... I guess that Roose Bolton allowing Jaimie Lannister to go back to King's Landing was a HUGE red flag about his alliances. Probably it was masked well enough for non book readers because he refused to release Brienne, charging her with treason and therefore showing some kind of loyalty to Robb, and anyway he was an enigmatic character enough, seen rarely, to have people go "yeah, whatever" at his choices. But still, with the benefit of knowledge, that was veeery suspicious.
- All the pain and grief that the Red Wedding brought was discussed at length, so I'll just point out a small comical moment: when Edmund sees his bride, sees she's smoking hot, and Walder looks at Robb with a smirk that says just with the eyes "See, asshole, what you missed out?".... you could almost like Walder there if not for, you know.... *remembers The Rains of Castamere starting to play* *cuddles up and tries not to cry* *cries a lot*
Anyway, the Red Wedding qualifies as "most exciting Dothraki wedding ever"