I really enjoyed that. Nice to see Alex and CL getting more to do after being underused all season.
I couldn't really remember how things had been left with Jeremiah and the Cadmus arc after S2 so I'll have to go back and check. I really liked how they dealt with Alex's anger, pain and grief over the whole situation with him and his death(s) and disappearances and working for an evil organisation. And as much as she adores Kara, feeling like she was always in 2nd place to her both as a daughter and a hero. And how she knew pretending to be Kara and physically solving the day in the VR wasn't actually going to solve anything.
Really nice to see Eliza/Helen Slater back, it would have been nice to see Dean Cain back one last time but I'm not exactly surprised we only got a back view of VR Jeremiah.
DH did a great job as fake J'onn/Hank and JR was hilarious as fake Brainy, they really amped up the cheese and clichés of the whole thing. Nia was back to blink and you'll miss her. William was okay getting closer bit by bit to the truth.
I didn't mind the Luthors being entirely off screen for once at all, although Lex's shenanigans are obviously involved. AB did a great evil smirk at the end.
I missed Kara more and it felt weird but better than I imagined. They might be able to work a few more Kara-less episodes in without me rioting if needs be with MB's pregnancy, which I was totally against before. Although who knows what's going to happen between that, the current shut down and writers.
It was very nice to see more Kelly than usual, both as Alex's girlfriend and pushing the ON/Lex plot forward, although their relationship is still very much "there" for me neither good nor bad just flat.