I'm trying to stay in line with the question this time, so I'm grabbing the line-up from the OP:

Barcus Wroot
When I finally met him again, it took me a moment to realise that he was THE gnome we had saved at the blighted windmill. By the time I'd hit the Shadow-cursed lands, my first forages into the Wilderness were a bit of a blur, because I'd intended to play BG3 in multiplayer with some old mates whom I waited for, dallying around here and there, and I could only play on weekends. Coming from AD&D 2e, my first thought was probably "What's a Svirneblin doing up here, and how did he end up up there?" Over the course of the game I not only started to appreciate Barcus as a gnomish being, but also as a purveyor of nice wares and probably the gnome most faithful to the original vision of nice, good-natured deep delvers living in a cruel dark place.

Zevlor
Tieflings in BG3 differed a lot from my 2e-expectations, although a lot of it could be explained by in-game developments that happened during the 120-year gap between editions. In original Planescape, they were quite rare on the Toril, and generally though often unfairly distrusted, so meeting a Tiefling paladin from a community on Toril was one of those things that felt like progress. Neither my Tav nor me could believe he would betray his people like that and expected a plot-twist.

Korilla
When I first ran into Korilla, I wasn't sure the next morning if I had really seen someone sneaking around the campsite during the party or if I'd dreamt it or had a bugged animation. During that time I fully expected a Gur attack, Githyanki raiders or even random monster attacks in camp, so this really rang the alarm. But nothing happened, so I kind of forgot all about it. I postponed investigating the Mason's Guild with the reconnaissance team and returned with the battle squad, but she was gone. When we met her again in Act 3, it took me a moment to recognise her robes, and since we weren't friendly with Rafael, there wasn't much to talk about and the place became a fiery toxic mess. In the end, I really would have loved to save her, and if for Hope.

Raphael
I always thought sending a powerful villain early in the game to tell PCs what to do can easily become railroading and should be done right. Sava didn't even want to think about why her eye was itching, and I thought that the last thing we need is some one-sided deal with a powerful Baatezu compromising us when we have a main goal already. One major reason why my Tav and Astarion didn't get along during Acts 1&2 was Rafael and what to do with his proposals. Due to some missed DCs we also never found out who build the Gauntlet, so while it all unravelled either pretty much as expected or retrospectively for me, I still think the character and his story are amazing!

Alfira
There are some people who think better of you than yourself, and in BG3 Alfira is definitely one of them. When I met a Tiefling bard, it was once again a "Wow, things changed!"-moment, in a good way. I felt that her positivity towards my Tav was maybe a little over the top for how things went, but getting to be a celebrated hero of the hour was one part of the explanation why my mean-spirited githyanki necromancer softened up towards the Tieflings.

Voss
Being able to play a githyanki was part of BG3's lure for me. I already had plenty of material on them but since my players don't like astral space, I never had any real use for them beyond being the red tape around really weird areas or not-quite-random encounters to hurry players along. Seeing how they'd work story-wise in a physical setting in 5e was therefore a nice inspiration for my own games and I also didn't sail without a map in this case. Knowing we should probably avoid githyanki patrols until we know more about our condition, running into them wasn't something I was looking forward to. Our first meeting happened when Lae'zel was in camp, but I thought it weird that he'd simply send Sava off to her Crèche and wouldn't implore further into the fishy mess of our story. After the meeting it was quite clear to me that we'd take the furthest route around Crèche Y'llek. Until his motives were revealed, I was never quite sure whose payroll he was on, but really got to like the beaten warrior wanting to do the right thing.

Wulbren
I guess with this chap I went from thinking he's a silly megalomaniac and maybe not a gnome at all to fearing he could jeopardise all our carefully laid-out plans for taking out the Absolute, and if by trying something stupid with the forge. His hunger for power may not be quenched, so I wouldn't be surprised if he'd be BG4's main antagonist.