Here are mine

Season 1

Eleven's "sacrifice"

Season 2

Mike and Eleven reunites

Season 3

Hopper's "sacrifice"

Hopper's letter

Season 4

Max's letter

Eddie's death

Max's death

I don't really get emotional in S1 but in S2

Mike and Wills whole dynamic

In S3

The sauna scene and Billy's death

In S4

Max's letter

Max's death

Eddie's death

Here are mine-

Season 1-

Joyce talking to Will through the Christmas lights.

Mike says goodbye to Eleven.

Mike's and Joyce's reaction when Will is presumed to be 'dead'.

Season 2-

Will shouting to the Mindflayer telling it to go away.

Eleven and Mike reunion.

Mike telling Will that being his friend 'was the best thing he had ever done'.

Bob's death.

Season 3-

Will destroying Castle Byers.

Billy's death (Max's reaction had a greater effect).

Hopper's fake death.

Eleven reading out the letter that Hopper had wrote to her.

The Byers moving to Calfornia.

Season 4-

Max's letter to Billy.

Eddie's death.

The van scene when Will cries.

Hopper and Joyce reunion .

Jonathan telling Will that he'll accept him no matter what.

Eleven fighting Vecna.

Max's 'death' (especially Lucas's screams).

For me the most emotional scene in S4 were Jopper Reunite, Max's death and Eddie's death.

I'm still have eyes full of tears when I watch these scenes.

Yeah Billy death was sad due to Max reaction