BG3 and the fun of transparency

[Telok]

we did that? not in my experience.
if i have to pick something vaguely familiar in that, it's the "hit with basic until it falls"
wait, that clearly refers to 5e, while my experience is 3.5. so ok, not totally relatable...

Basically that last sentence. Its a D&D 4e & 5e thing where what a npc/monster is and does is unrelated to the description and type. For example, in most games and D&D 3.x size has a rules defined effect making bigger critters stronger and smaller critters more nimble. Players can use that to prepare tactics. Likewise in 3.x undead have specific traits & weaknesses that can be planned for or exploited.

Without that consistency describing a monster as "a huge hill giant zombie" doesn't actually mean much of anything because the words "huge" and "zombie" don't carry that information any more. You're now facing a bag of hit points with some attacks and any special abilities the GM or writers wanted to throw on. The "huge hill giant zombie" is just as likely to have a good dex save, resist fire damage, and have a 15' reach as it is to have a bad dex save, be vulnerable to fire, and have a 5' reach.

It wouldn't be as bad if it were just a few outlier critters that broke some guidelines. But the npc stats are so divorced from anything beyond hp/ac/dpr and there are so many unique mini-rules in the thousands of stat blocks, that many of the descriptions are as useful to the players as "a person in armor with a weapon". So much information is hidden from the players by the lack of consistency that you can't practically plan anything but the most generic tactics like "haste the fighter and spam damage".