You're asking me to remember stuff from the beta of a game 4 years ago, which changed repeatedly and rapidly over that period, so I hope you will be okay with me being vague - people have been finding screenshots from their own EA periods and being astonished by what's in them lol.
But some examples:
1) There was an encounter with a dying Mind Flayer not long after you got off the ship - it's still there - but it had a bunch of fisherfolk around it, being mind controlled for no clear reason. In very early EA, there were only lose/lose outcomes to this. Whatever you did, something horrific happened, usually you having to kill all the fisherfolk, regardless of whether you stopped them being mind-controlled. And the companion characters had some pretty weird and callous comments about it. This left a pretty horrific impression, and not in a good way - it operated as a sort of mission statement - "Everyone is bad and everything will end badly", especially as it was essentially the first non-companion encounter outside the Nautiloid. Over the course of EA, they toned this down twice, first making it so there were some grey outcomes, but they required multiple DC15+ saves/checks to get (not easy at L1/2) - and at this point you couldn't save game in dialogue, note - but it was still pretty bad. Then by lowering the DCs but you still had a lot of rolls. Eventually they removed it, and put the fisherfolk down the map, but still had a pretty hostile encounter with them, then they removed that too, because it really wasn't serving any purpose.
2) The Nautiloid itself used to be longer and more detailed, and also used to be much more likely to involve you being forced to a bunch of innocent mind-controlled people by accidentally or even unavoidably aggro'ing them, which felt pretty bad. When they shortened this to make restarting less tedious, they took I think all of that out (NB knocking people out was either not in the game or so well hidden almost no-one knew about it, at this point), and now you only fight devils (or optionally a couple of Intellect Devourers).
3) All the companions were bigger jerks. Shadowheart was intensely rude and unpleasant (not "sassy" as I have seen people try to retcon - just unpleasant and sneering like she is to Lae'zel early on), and the only way to get past this was to act like she was your boss and you were the world's most brown-nosing employee. I hate to use the term "simp" but basically unless you took that attitude on literally everything she said, she acted like she hated you. You could do a bunch of things to help her, but unless you also went along with 100% of her nonsense, she hated you. They dialled this back over time, particularly in one big patch were they added reactivity to you saving her from the pod - that was the big turn-around. Gale was prissier and more superior. Lae'zel was... mostly the same but had no context - you couldn't get nearly as much info about WHY she was behaving like this. Karlach wasn't in the game for a lot of EA, and only meetable not possible to recruit for the rest - but she was pretty different - a lot angrier and bitterer - like her darkest moments in the real game were basically the norm (a lot of that is from data-mining to be fair). Wyll was a different character with a different, and frankly grosser and weirder story, where he was the one lying to people, and Mizora was kidnapped (?!?!?!). Astarion was similar to Lae'zel in that he changed less, but lacked context for his behaviour. He was also more aggressive and callous, and didn't have anywhere near the number of funny lines.
4) All the NPCs were bigger jerks. This is a bit hazier but virtually every major NPC gave you a harder time, through a combination of higher DCs on any checks you needed to make, more checks, and just being less pleasant when you helped them, with a lot of "Hmph I didn't ask for your help"-type stuff - I think even Zevlor gave you quite a lot of attitude back then.
5) Again more hazy but a lot of quests and situations which have a positive outcome now simply didn't have one back then. They just had different bad or at best grey endings, and again due to the DCs for checks being higher, and there being more checks, even those tended to be more difficult to get.
6) Mechanics-wise, NPC enemies and spells in general tended to do a ton more with creating surfaces (fire, ice, water, etc.) - like stuff now where you only get a surface effect with special items or interactions with objects in the world, spells just did and NPC enemies often had grenades, arrows, barrels, etc. that made surfaces - more so than they do even on Tactician now. Compounding this, the surface effects were much more powerful - I forget how much damage "Burning" did, for example, but it was definitely a lot more than 1d4/round lasting for at most 2 rounds (assuming you got off the surface). The actual D&D rules were significantly less well-implemented (you can sort of trace this from the patch notes at least), and they tended to get overwhelmed by the wild plethora of surface effects that went off everywhere, like even blood was a major issue! Larian got such negative feedback here that they started toning it down pretty rapidly here. NPCs also tended to have more "hard" CC spells and higher damage spells at lower levels, like it seemed like Larian weren't quite ready for how few HP player characters had in D&D - the game wasn't exactly harder though because the surface effects were much easier for a player to exploit than NPCs. People complained a lot that it felt like DOS3, gameplay-wise, not BG3, and they were right to.
7) "Daisy" vs The Guardian - I won't go into too much detail because I'm not sure how much of a spoiler thread this is, but there was a totally different approach to the tadpoles, which seemed to be more like "Daisy" (who you created, like you create the Guardian now, but they asked "who do you desire" instead of "who protects you" or w/e) was trying to tempt and manipulate you into using and where using any at all was a big deal (also the tadpole powers were class-based), and it seems like there was a separate unseen voice trying to convince you not to (who in retrospect might have been Orpheus). Overall this was the one bit which wasn't more grimdark, but it was pretty different and seemed to be pointing to a later game where the main question would be "What will you do for power/to win?", which is definitely not where the game actually went in the release version. The whole song "Down by the river" is for/about Daisy, note. Also you gained power with the tadpole by using its power, not eating other tadpoles.
I think that's enough for now lol.
