Any good tactician would have started the battle with a dragon airstrike. That would have reduced the enemy considerably. See also desert Storm. The poor Dothraki were thrown away, for all their loyalty. If Melisandre hadn't shown up to light their blades, they wouldn't even have had weapons that would have worked!
A flanking attack by the Dothraki like the one by the Rohan in The Return of The King, could have gotten better results.
Those pits with stakes were effective in the sense that they broke up the en mass charge by the undead towards the defenders. The defenders should have kept behind the pits and the Unsullied could have picked off any undead, making it through, with their spears. Then the dragons could have have lit up the pits.
Regarding the major deaths,
Lyanna Mormont : I was sad to see Lyana Mormont die but she went down like a Boss.
Lord Commander Edd Tollett: The Last Lord Commander of the Night Watch died. His death is poignant in the sense that the Order is needed no more. He was a good and decent man.
Melisandre : She was useful as a Fire Starter at a Barbecue. She did make Arya realize her potential towards the end.
Jorah Mormont : It was the saddest death for me And i think that Daenerys just lost the person that she can trust the most.
Theon Greyjoy : He died a hero. Yara would be proud. Even Euron, i suspect, would think better of him now.
Beric Dondarrion : I actually liked him. He was religious but also likeable. He would be drinking with Thoros of Myr in the Lord of Light's heaven right now.
Night King : How little we knew him. I would love a backstory about him.
Special mention :
Viserion,
Lady Karstark and the
Dothraki advisor, Qhono.