Larian has been absolutely phenomenal through their process on both of these. Kept with the ‘it’ll release when it’s ready’ model, the exception with the alpha/early release on BG3 which I would say helped improve the quality of the Release product that much more, through testing/reports and cash influx without the ‘pre-order today, get whatever you get tomorrow’ mantra.

The most significant change I noticed was you can cast any number of leveled spells per turn. That’s a pretty significant shift from 5e’s rule of only one leveled spell (excluding using action surge if you dip into fighter) per turn.

However it makes the player stronger so I doubt anyone is really complaining about it.

It’s faithful enough to 5e that my partner and I broke out the players handbook to do some long term class planning together. A couple of things are different, like buffs to frenzy barbarian and changes to roleplay feats or spells to have a more mechanical benefit.

But yes, as a long term DM for 5e, it’s faithful to 5e.