I feel like the game does a good job of adapting the 5e ruleset into a video game format. The core classes, abilities, saves/attacks etc are recognisable.
Is it a direct copy - no, and neither should it be because 5e is a different medium with its own set of problems. Plus, 5e streamlined many mechanics to make the game more accessible for both players and more importantly - DM's. And that is good, since I was introduced to DnD 4e and hated that thing.
Saying that, some features can be brought back in a video game because they don't make the game harder for the players - for example burning damage.
Furthermore, the game can play around with features that are less prominent in DnD games and that is vertical combat. I don't know about you, but I design 5e encounters mostly on flat maps, where keeping track of height is a pain. Furthermore, I don't think busting out Pythagoras theorem to figure out whether your spell can reach an enemy is fun. And 5e is built around encounters being flat, which BG3 thankfully does away with.
Also, I am sure Larian knows what it is doing and judging by the numbers of Early Access sales and Twitch streams BG3 will perform well.
