1. UI is too big, unnecessary big. Can cause problems if played at not wide-screen resolutions. It all can be neatly placed in a single line (maybe two, rather thin lines), like in DOS:II, the best isometric RPG on the market. Why you want so much to be so "different" from DOS:II? It is the best, so take the best from it, and build on top. Don't listen to whiny fools who say that "it resembles DOS:II too much", it is a compliment. Remember UI from worldwide gameplay reveal at PAX? It was a very good base to build on. Just enhance it (there was two lines, but second was basically empty, huge health/movement bars, huge icons of effects on top of the portraits, map was not good, now it's better). Fully adjustable single/double Skills line(s), where you can put anything, this is the perfect UI. Not a bunch of sections, with unnecessary "design" elements.
2. Portraits. First, I don't need 2 portraits in my UI, one in corner (party) and one in the middle of the screen. I see whom I've chosen, I don't need additional clutter portrait in the center. Secondly, portraits now look like it's renders of naked models. Third, add casting spells on portraits.
3. Add books. Many books. Game is empty now, give us some LORE, there is a lot of D&D Lore.
4. Add full descriptions of Spells, when you learn it as a Wizard, Lore description. Like "Polymorph 4th-level transmutation Casting Time: 1 action Range: 60 feet Components: V, S, M (a caterpillar cocoon) Duration: Concentration, up to 1 hour This spell transforms a creature that you can see within range into a new form. An unwilling creature must make a Wisdom saving throw to avoid the effect. The spell has no effect on a shapechanger or a creature with 0 hit points. The transformation lasts for the duration, or until the target drops to 0 hit points or dies. The new form can be any beast whose challenge rating is equal to or less than the target’s (or the target’s level, if it doesn’t have a challenge rating). The target’s game statistics, including mental ability scores, are replaced by the statistics of the chosen beast. It retains its alignment and personality. The target assumes the hit points of its new form. When it reverts to its normal form, the creature returns to the number of hit points it had before it transformed. If it reverts as a result of dropping to 0 hit points, any excess damage carries over to its normal form. As long as the excess damage doesn’t reduce the creature’s normal form to 0 hit points, it isn’t knocked unconscious. The creature is limited in the actions it can perform by the nature of its new form, and it can’t speak, cast spells, or take any other action that requires hands or speech. The target’s gear melds into the new form. The creature can’t activate, use, wield, or otherwise benefit from any of its equipment."
Also, in-game, explain on what exactly you need 50 gold to learn a spell, add some explanations, like a DM would do.
5. Add some crafting. Artificers can craft A LOT of stuff in 5th ed. (arrows, potions, poisons, grenades, armour, etc.), basically, "on their knee", can infuse items with magic, attune magic items, craft a magic items with different levels of rarity, Wizards can scribe scrolls, so add full on crating system in the game, please.