Personally, I enjoyed the finale, so whether it was "badly written" is subjective, not objective or quantifiable.
Let's talk about Nightwing for a bit.
I am sure I missed a story arc or two in the comics over the years, but I was never comfortable with what they gave us with the Robin/Nightwing transition. Robin WAS Dick Grayson. Over the years they emphasized over and over his costume, identity, and motivation as coming from the Flying Graysons. It makes sense that he would mature, deal with it, and move on, in a way that Bruce was never able to. What I could never wrap my head around was how every new sidekick was running around in a Flying Grayson's outfit and Dick was in junior Batman colours.
I really enjoyed the way the season developed Dick and showed us how he transitioned from Robin to “not Robin” to Nightwing, as well as his interactions with Jason. It made sense, to me, finally, that this is how it happened. My problem with the whole idea of Nightwing was that if he didn’t want to be Batman junior, why would he ditch his family’s colours and become Batman 2.0?
Everything in this season that happened to Dick finally told me the story about one of my favourite characters (comics, novels, TV, movies) that I wanted to experience. The hallucinations with Bruce and the resolution scenes between them gave me closure about their relationship, and how he wasn’t walking away from the idea of a Batman, he was moving forward with it. Great season for me.
ETA, I didn't believe for a second Donna would stay dead. Let's see what happens.