I finished the series on Saturday. I was initially nervous about Netflix's decision to release all 13 episodes at once, because they won't be able to build up anticipation, but I think it worked to their advantage. Everyone is talking about it, and the people that want to binge through them are able to if they want. Plus, the season ends on a cliffhanger.
I was shocked that Frank would kill Russo, but it makes sense. He killed the dog in the first episode, putting it out of it's misery. Killing Russo would be the logical next step, especially because of all the troubles Russo had caused himself. Which was another thing that surprised me: Russo was on the path to recovery, but he never really bought into it. He never spoke up at the AA meetings, so it was a matter of time before he relapsed.