Oh I love love love ER.
Fave episodes are definately the one where Lucy and Carter get stabbed.
The one where Lucy goes to beg Romano for the mechanical heart and then the patient dies.
The episode I think is named 21 guns where Sam's ex kid naps her and theres a shoot out when abby realises something is up. Sam just says " thank you abigail" and she twigs. Kovac is tied to a bed then has to watch abby collapse through the window. Their son is delivered prematurely and abby nearly bleeds out.
Then theres the one where sandy dies. "please, shes my wife" so sad.
The one where genie treats an elderly lady and keeps quiet when she discovers that her husband "killed" her. They had planned it for ages and hed helped her get up and dressed and do her hair and make.up ready.
The one where pratt dies is also really good. That tear that runs down his cheek when he realises that hes probably going to die as they try and clam.off the artery in his mouth. And that slow.walk to the elevator lead by his brother... and then they go have that party for him after in that dive of a bar eating mozzarella sticks...
The one where carters baby died. Shes so relaxed not worried at all thinks.the baby is just asleep. Only goes to the er because Carter makes her. And then.....
ER always tackled the hard issues. Euthanasia, racism, homophobia, psychological issues, addictions etc. Done really well.
The one where theres that elderly couple and kovac breaks the rules when one tells him shes been her girlfriend for decades but then Weaver by law still has to call a brother who hasnt spoken to his sister in forever because the law didnt recognise their relationship and instead if letting her go like she wants they have to stick her on machines.
I think ER formed the basis of alot of my ethical arguments/points in humanities debates in school 
