Season 3 was just plain awful... (Spoilers)
Not surprising considering they stopped following the books and just made up their own stories for the most part. Probably be an essay if I wrote all the problems I had with it, so I'll just summarize them.
- Felt like it dragged on forever. I was excited that it was 10 episodes instead of 8, but it had so much more filler than previous seasons that led to quick and disappointing endings for all the plots.
- The maudlin interactions between Uhtred and Alfred and Uhtred and Brida. Completely against the spirit of the books.
- Uhtred's maudlin speeches. Just so absurd. Such cringeworthy stuff.
- Uhtred putting a knife to Alfred's throat was so over the top. Never happen.
- Uhtred and Aethelflaed are supposed to have an epic romance in the books. It's reduced in the series to Aethelflaed awkwardly kissing Uhtred like a smitten schoolgirl. They put more time and effort into her relationship with that annoying advisor. And Uhtred and Brida who utterly hates him.
- I've said it before: The actress playing Aethelflaed was completely miscast. She looks and acts nothing like her in the books. She's dull and she's not beautiful or golden-haired. It's so distracting how not like Aethelflaed she looks and acts.
- Skade was a caricature. Her character was interesting for the book she was in, but they changed everything around and she was nothing but some angry little girl. A character more suited for The 100 on the CW.
- Everything concerning Æthelwold and Ragnar. How and why they came up with this plot is beyond me. Completely against the spirit of the books. Pretty much everything concerning Æthelwold has been absurd from the start. He had a lot of support, he wasn't a drunk loser.
- Aethelred is made to be a nobody. They act like he has no authority. Makes him seem like no threat and a bumbling fool. In the books, Aethelflaed is respected by the Mercians, but he has all the money and power. When she tries to raise the nobles of Mercia without him, none support her over him.
- Leofric's aggressive ghost and the idea that Uhtred owes anything to Wessex or Alfred after all he's done and the way they treated him is absurd.