Yeah, the Castle arc was strong as hell. The show manages to hit a lot of good character beats, and they f-ing nailed the casting for Matt and Foggy. It also didn't suffer from Jessica Jones's major flaw (and, to a lesser extent, DD season 1), which was how much the plot slowed down during the middle while they fumbled for something to do. I never noticed the show drag like those two. And, for clarity, I liked JJ, but that's the consensus criticism that I agreed with. It would have been tighter with, say, 8 episodes instead of 13. The two major plotlines in DD S2 helped with this.
My instinct was to agree with Newjak above me about the lack of tying together the two arcs. There's a satisfaction to that sort of thing, no doubt. But I also think we're sort of programmed to expect it (I certainly was), so in an intellectual sense I admire the choice not to shoehorn the two together. It made for a different viewing experience.
Elektra seems the biggest lightning rod for division. I was mostly ambivalent to her performance. My biggest gripe was how convoluted the Black Sky stuff got. Maybe they were pulling from the comics - I never followed DD comics too closely - but it seemed overtly confusing at times, bordering on nonsensical toward the end. The other lone element - though it was much smaller - that briefly pulled me out of it was Castle's house. In what had to have been months, nothing was moved out? No one was monitoring it? Very weird.
Good show. Psyched for the inevitable S3. I won't quite join the chorus calling for a Punisher spinoff, though. It would be fine, I'm sure. But there's an art to leaving people wanting more. Marvel's best use of him may be in cameo roles.