I really liked this season. Was it perfect? No, but it kept me engaged more than last season.
One of the biggest issues I had was how easy it was for various members of the "good guys" to walk around the underground Russian lab, especially when it came to Robin, Steve, Dustin and Erica.
Hopper allegedly dying had me bawling. He couldn't have gotten back up to Joyce before she turned the keys because when he tossed the Russian terminator in the machine it created an electric wall between Hopper and the stairs. I'm not convinced Hopper is dead but I don't think he's the American prisoner in Russia either. I think the prisoner is Dr. Brenner.
Even he was a complete dick in season 2, I cried when El was describing the beach memory to Billy. I personally think Dacre Montgomery did a great job this season. You could tell that Billy was terrified of being controlled by the mind flayer. The sauna scene really conveyed that fear and remorse of the things he's done. El was able to give him peace before his death.
I'm looking forward to the next season.