After playing the game near 200 hours and giving another big modern 5e game a try (Solasta) I think I see what it feels like BG III is missing. Here's a brief pro con for the early access.
+BG III feels like a great homebrew campaign with many alterations to spells and spell-like abilities.
+Great work on cinematics and mocaps.
+Early mod support means early mod communities means great mods and health for the game!
-Non grid-based combat
+/- Party members are deep characters that are unique but feel like npcs made by the GM to support a player rather than party members. Although each character that was created for BG III is deep and intriguing especially on neutral and evil playthroughs, they feel less like characters at a table made by players and more like npcs made to flex in moralities with the players actions. This could be due to the limitations of EA but as of this moment the only character in game that doesn't come across as a neutral or evil aligned is strictly Wyll (who is clearly chaotic good) in the early state the game is in, forcing certain parties to form (no good aligned warrior to balance a party as La'ezel is designed as a jedi devil's advocate and is the only non-player warrior type in game atm). Shadowheart tends to come off less like someone aloof and secretive (as what seems intentional knowing her story thus far) and instead just seems like a real jerk (which leaves no healer option). While I personally am a fan of trying to get everyone together to ensure they don't undergo ceramorphosis (or maybe something worse baring spoilers) at some point, I am keenly aware it can be a bit of a turn off of the game for particular characters harshly judging every choice you make and may fight you to the death at some point.
+combat is ferocious and tactile with many options for combat solutions and styles.
-Something BG III is missing for combat is readied actions.
-disengage should be nerfed and restricted to a feat, incorporated with roguish-classes for balance probably.
-cover system is unclear, missing, or intentionally excluded.