-Separate ASI and feats. ASI are too important to miss out on, but feats add uniqueness and specialty. Even/odd number ability scores from feats and their usefulness could be worked on.
-Half (3/6) of the caster classes use charisma, yet only two feats that isn't race specific adds charisma. In comparison, only one caster class uses intelligence, yet there are four non race specific feats that add intelligence. Are they even trying?
-Add more feats, and not just race specific. Some races have many feats, others have none. They add more variety in builds.
-Classes and more importantly sub classes need to be way more unique. Better balance, and more variety and options. Beast master, wild magic, berserker, four elements, cough, cough... Really bad execution of concepts.
-Balance classes for refreshed abilities on short rests. Every class should benefit from short rests besides healing, or no one. It's a really awkward mechanic for a party as it exists now.
-Spell overhaul. Remove redundancy, and balance the rest. There are a lot of bad spells in every spell list, and a few jems. Faerie fire is insane, and no official errata for healing spirit, really?
-Marital classes like battle master are great but flawed. Manoeuvres should be like spells, better ones are locked by level advancement. You take the best manoeuvres at level 3, then picking lesser ones later.
-Most classes need more bonus and reaction spells and abilities. Valor bard bonus action attack is a step in the right direction.
-More options for character creation that gives more opportunities to do variable things both on the battle field and for role playing that are class specific.
-Remove rangers favoured enemies, it's junk. I know it's a staple, but it's time to pull that staple.
-More skills and abilities that add advantage or disadvantage. Faerie fire adds an AOE, save or suck, 25% hit probability increase to an entire party with a 1st level spell only available to two classes.
-Also the way D&D material is written has always sucked in relation to rules. An example: Advantage or disadvantage. Almost no skill or ability plainly says it adds advantage or disadvantage, they'll say it's adds a condition. Then you need to know what that condition does, which is advantage or disadvantage. D&D material is famously bad for this.
-Things like unlimited cantrips, manoeuvres, metamagic, fighting styles, and invocations are great. They add variety to class builds and play style. More of this please.