It lacked the mystery and originality of the first season. That was a phenomenon. Everyone was talking about the upside down and I nobody knew what was going on. It was scary and fun and fantastic.

The second one was closer in tone to the first but not as good.

Season 3 was more of a family crazy 80s adventure against a monster and Russians. (With some added gross and gore). It lost some of the mystery of the first and went more for the fun.

That said, I LOVED IT. It felt like it was custom made for me with the humor, action, fun, and 80s references. I loved the Back to the Future stuff and the Terminator stuff - especially the music cues. Other things I loved:

Neverending Story
Hopper dealing with Elle's relationship
Dustin's "Imaginary" Utah girlfriend
Starcourt Mall
The evil Russians
Steve the hair Harrington
Billy being evil. And then Eleven helping him find his humanity so he could save her
The sappy ending that made me cry