Rather too many people here getting frothy over changes from core 5e rules. Larian do their own version of 5e rules. Elemental surfaces are fun, make the map layout and positioning absolutely crucial, and allow for much more tactical play. Some people get hung up on minute differences from 5e: maybe enjoy the game as it is, if it doesn't work in the game, then critique it in those terms. 5e isn't a bible and it's not useful to be fundamentalist.
I played D:OS 1 and D:OS 2. I enjoyed D:OS 1 and D:OS 2. This is a bad "hot take". I'd even call it a strawman argument.
For starters, Larian themselves have advertised this game as being based on the D&D 5e ruleset. They did not say "Based on the Divinity: Original Sin rules."
Don't tell people to stop complaining about the differences between 5e and this game. Larian does Early Access for a reason, which is specifically to get feedback. If you like the system as it is now, great, fine, that's feedback, and you are free to give it. Don't tell others to shut up.
I will now explain the reason for the complaints. It is not a reflexive, knee-jerk aversion to change.
Divinity: Original Sin 2 is balanced on the idea of being fully charged with all abilities available for each and every combat. Tactics are King.
Dungeons and Dragons 5th Edition is balanced on being fully charged after a long rest, and then having resources and options slowly whittled down over the course of a day. Resource Management is King.
BG 3 is using Hit points, Armor Class, and Spell Slots for players from D&D 5e. They are using the Concentration mechanic from D&D 5e.
Monster HP in BG 3 is usually higher, Monster AC is usually lower, and Ability scores remain the same.
D&D's HP, AC and Concentration is not balanced around the idea of status-inflicting surfaces, status-inflicting attacks, and AoE attacks to be as prevalent as they are in BG 3.
Just about every single surface effect in D&D has some kind of saving throw to resist for half or no damage. There is no such thing as a guaranteed hit from a surface in 5e, but there is in BG3.
Concentration spells are balanced around a roll under 10 or half the damage losing concentration. The more checks you have to make, the greater the chance you will fail. You are far more likely to fail checks because you're doing a lot more of them.
Enemy HP is way up, enemy AC is way down. This makes spells balanced around on hitting AC more reliable. This makes spells which affect a certain amount of enemy HP far worse, such as Sleep and Color Spray, because they can affect fewer enemies.
Enemy saving throws remain the same. This makes spells balanced around enemies failing a saving throw will seem to suck more because they're doing less damage. Example: Sacred Flame - it does 1d8 - an average of 4.5. Fire Bolt does an average damage of 13.5 from what's supposed to be a 1d10 spell.
Armor Class is based around advantage being relatively rare. Statistically speaking, Advantage is an effective +4 (Disadvantage an effective -4). Constant advantage from high ground is and disadvantage from low ground means those on the high ground are dealing more damage, those on the low ground are missing more and dragging battles out longer than would be normal.
And I'm even leaving out bonus action shoves, disengages, and hides.
Larian has changed many things from 5e, but have left other things as standard. That does not work. The systems have different design goals in mind.
Nice summary! And also constant advantage from backstab.
