People feared for Eddie's life from the very beginning, and they turned out to be right. That's exactly why they are mad now.
Long before the premiere of Volume 2, the imminent death of Eddie Munson was almost an open secret among fans. Everything was leading up to the Hellfire Club leader not making it in the end: him saying that 1986 was going to be "his year", dropping lines like "Don't ever change, Dustin Henderson", hinting that he has always been a coward who would rather run away than face the danger.
Naturally, the final two episodes showed us precisely what we feared but expected: after a bombshell guitar performance on one of the Upside Down's rooftops, Eddie Munson exited the stage, sacrificing himself to save his friends.
And fans are furious because of that.
A new likable character dies at the end of the same season he was introduced? That's "predictable and pointless" if you ask fans, especially after all the times it already happened in previous seasons.
Moreover, the sacrifice itself seemed poorly executed to many people. For instance, one Reddit user pointed out that Eddie decided to throw his performance to distract the monsters even without actually knowing that the gang needed more time.
"I wouldn't have mind Eddie's death that much if it actually had a HUGE impact, but it didn't," another fan wrote.
But there is one bright side – if we may – to Eddie's death even to those frustrated with how it was handled by the writers.
"I see a lot of people being disappointed about Eddie's death and I am too. But how could Eddie reclaim his innocence? No one would believe that he wasn't part of this. People don't know about the Upside Down. They think that this is a gate that leads to hell and they think that Eddie is part of it. No one would believe otherwise." – /Chris2005Writer.
The main characters, however, have once again miraculously survived the epic showdown, although Max ended up in a coma after being captured by Vecna once again. All clues point to the final battle taking place in season 5, as Vecna is still alive and relatively well.