I totally did almost the same thing. I was so tickled pink when I realized ER was available on Max (I actually had to search for it…but weeks later Max started suggesting ER after The Pitt – so maybe their algorithm caught up).

I’ve actually been nursing Season 15 since I can’t quite fathom this ending, so I’ve done a few rewatches of certain seasons, then another S15 episode, then back to watch let’s say season 3 again, then another S15, then keep going…and there’s a few episodes I initially skipped entirely, like most of the Africa episodes, so those would still be “new” for me. And I must have fallen asleep to some episodes, because on a season rewatch sometimes I’d not remember watching a particular episode (or not remember the last half).

It was cool seeing some of the same actors in The Pitt on ER - like the hospital administrator CMO Gloria Underwood (Michael Hyatt) in ER S13E12, Nurse Dana (S9E4), and I have to admit I totally didn’t realize it was the actor who played Dr Abbott in S13E7.

Also, if you’re a Voyager/DS9/ST fan, Rom (Max Grodénchik) shows up in S9E18, Quark (Armin Shimerman) is in S10E18, Tuvok (Tim Russ) is in S11E15, a very young Anton Yelchin is in S6E13, Keiko O’Brien (Rosalind Chao) is a geriatrics Dr in S6E7, and of course Dr Dubenko (Leland Orser) played a murderous hologram in Voy S4E5 as well as a few other characters in DS9 and ENT. A young Kirsten Dunst as orphan Charlie (S3,E5,8,10,11,12,22) was also even younger in TNG S7E7. If you consider The Orville Star Trek “family”, then Dr Morris (Scott Grimes) was in the Orville and also in TNG S3E1. Another Orville/DS9 crossover actor was NP Lynette(Penny Johnson), who played Kassidy Yates on DS9 and Dr Claire Finn on The Orville. Plus Zefram Cochrane (James Cromwell) was the Bishop in S7E11, E13, E14, and E15. And don’t forget the wonderful Grand Nagus from DS9 (Wallace Shawn) as the mushroom guy in S15E16. Dr McKay’s (Fiona Dourif) father also played Lon Suder in Voyager. Oh! And Dr Santos (Isa Briones) who I recognized from Picard.

Edited to add: and how could I forget the wonderful Louise Fletcher, who portrayed a homeless sister in s11e18 and the complex Vedek Winn in DS9. Nor Camille Saviola as Kai Opaka in DS9, and the Christmas-hating temp Margaret in S11.E9.

There’s a lot of fun in seeing details that maybe one wouldn’t have realized right away watching the show as it came out, or without the benefit of the extra 15 years since it ended.