I imagine some Karofsky fans were very excited when they heard he would be back. I'm sure they are let down that he was just in Rachel's nightmare. Jacob ben Israel was in it, too, but I don't think those people feel the same way about Jacob as they do about Karofsky. Becky was in the nightmare. Rachel's friends were in it, too, dressed in clothes they'd worn much earlier on.
Kurt was in the outfit he wore when he and Rachel had their first Diva-Off with "Defying Gravity," in "Wheels" (season 1, episode 9). Chris Colfer is three or four inches taller now. I believe I also saw something that said that he'd lost twenty pounds since then, too. I think his shoulders are broader, too. I don't know how they get him into outfits Kurt wore early in season one. In "The Break-Up" (4.04), Blaine imagined Kurt in the outfit he'd worn when he came to Dalton for the first time, in "Never Been Kissed" (2.06). Chris Colfer probably got a good couple of inches taller since "Never Been Kissed." He was probably about 5'7" tall when the first season started. He was possibly eye level to Blaine when he and Blaine met, and Darren Criss' height is given at a possibly generous 5'8". Chris Colfer is at least 5'10" tall now. It's fortunate that Kurt rarely wears the same outfit twice.
Blaine wore his Dalton blazer. Tina was in Goth clothes and had a stutter.
Tina actually did come to see Rachel's opening night. Will came, and Sue went along. Will and Sue sang themselves to New York City. When I saw the snow globe of New York City, I wondered if they'd sing themselves there. Rachel did in "Goodbye" (3.22) and Santana mid-way through season four, and Blaine and Sam when they visited in "Movin' Out" (5.06). So either Sue or Will still has some magic. I had thought the magic had left McKinley, but there's still plenty of magic in the Glee version of New York City. Kurt is there.
Will had to leave before the show started because Emma had gone into labor. Emma wasn't shown. They named the baby Daniel Finn Schuester.
There was a flashback to Finn when Rachel sang one of the last songs in the show. I didn't expect it, but I guess I should have. It didn't make me that sad.
Sue walked out of the performance early on to have an encounter with a man she saw when she entered the building. They had sex in all corners of the loft. The man came out from behind a curtain wearing Kurt's bathrobe. He asked where Kurt had gotten the bathrobe, and Kurt said, "Keep it." I wouldn't have wanted it back, either.
Kurt was back to sleeping with Bruce, the boyfriend arm. So much for Blaine being there. That made me a little sad.
Glee still has the hallways of McKinley, and the principal's office. I thought they'd be gone, but I guess they'll be used again here and there.
The New York group went to a gay bar after Funny Girl. Rachel was recognized and celebrated there. It was a bar Blaine knew, in Greenwich Village.
All in all, for an episode with that much Rachel, there were still things I appreciated.
I later saw on Tumblr pictures of Blaine in the audience of Funny Girl, with Darren Criss' parents sitting right behind Darren. I didn't see it as the episode aired, but I'll look for it on a rewatch.