I like 5E mostly, and it is my favorite edition, but it has few flaws.
1. Short rests are not short. 4E did it better with 5 min rests
2. HD's for healing would be better with fixed value as in 4E.
Does not to be 1/4 HP but a fixed value as option for leveling up HPs. d4->3, d6->4, d8->5, d10->6, d12->7.
Plus con mod. Just to be more consistent.
3. Feats. This should be No.1 on the list, or last
feats are all over the place in power level.
While I only hold -5/+10 part of two feats problematic in some cases(having advantage on demand), they can be removed and replaced by giving +1 str/dex instead, most of the feats are not worth losing +2 ASI, hell some "full" feats are not worth losing +1 ASI.
All feats(if they stay in competition with ASI's in 2024) should be reworked as half-feats.
As with recents UAs, all characters should get a feat at levels 1&4 independent of their classes.
or remove feats from class resources, make them all half-feats without any ASI's, detach them from class(except for some bonus feats as a class resource) and make them available at levels:
1,1,2,4,6,8,10,12,14,16,18,20.
4. Abilities.
As racial fixed ability boost will go away, just make all characters have:
+2,+1,+1(half elf value), or +1,+1,+1,+1,+1. That is 5× of +1, as +2 to high ability should be worth 3× +1. And lack of a bonus to 6th ability makes possible to have a score of 8 on point buy. And with cheap scores(13) you could have a character of 14,14,14,14,14,10.
Limit the max ability to 18.
Yes, if you roll 18 you will have to put your floating bonus somewhere else.
Add some light armor of AC 13+dex to compensate for not having +5 dex mod possible. For some 500GP cost, so it is not available from the start.
Add +1 ASI at levels; 3,7,11,15,19. One(and only one) of those ASI's can be exchange for a feat(to fix any unfortunate odd total of ability scores). Max is still 18.
5. Add 10th level spells. Single spell slot at 19th level for full casters.
6. Rework warlocks and bards as 2/3rd casters:
spell levels at class levels; 1,4,7,10,13,16,19. Spell levels 1-7.
6b: rework maybe even druids and sorcerers as 2/3 casters?
Make their wild shape/summoning and metamagics with more usage and more power/versatility.
That will leave only clerics and wizards as full casters. As it should be.
7. Delete monk. Or make it work.
Right now a feat and/or fighting style can take care of unarmed combat.
8. improve 1/3 caster subclasses to 2/5th casters. Or getting new spell level every 5 levels instead of every 6.
at levels 3/6/11/16. Still limited to 4th level spells, but with slightly faster rate.
Then you can have classes with spell levels at class levels:
cleric/wizard, 10 spell levels, at class level;
1,3,5,7,9,11,13,15,17,19
bard/druid/sorcerer/warlock, 7 spell levels;
1,4,7,10,13,16,19
artificer/ranger/paladin, 5 spell levels;
2,5,9,13,17
arcane trickster/eldritch knight/some new non caster subclass(barbarian shaman or a monk); 4 spell levels
3,6,11,16
9. Increase damage on non finesse weapons, especially with 2Handed or return 1+1/2 STR bonus on 2Handed melee weapons that are not finess.
10. crits double all damage. Yes, even the static bonus.
11. Return AoOs for making ranged attacks and casting spells that are Action long or longer. Bonus action and Reaction spells are free of this penalty.
12: Making a ranged attack will cause that all melee attacks on you have advantage until your next turn.
13: morph Cure wounds and Healing word into a single and better spell.
Bonus action, range 60ft, heals 2d6 per spell level plus casting mod, target must spend an HD for every spell level, additional healing normal for HD, every spell level of healing with this spell that is not supported by spending an HD will heal for minimum amount(2).
Same with healing potions.
I.E. a barbarian/paladin has a d12 and d10 HDs left. He is healed by 4th level Cure spell.
he reagains d12+con plus d10+con plus 4d6+4, 4 is instead of 4d6 as not being supported by HD healing.
With Con of 16 and casting mod of 16 that is 36 HPs on average.
if the barbarian had 4 d12 HDs available, it would be 69

or few points higher if we use fixed HD healing.
Give all healers something fun with their Actions.
14. Usage of potions/oils/etc is Bonus action when self applied.
14a, same for Paladins Lay on Hands
15. get rid of medium armor.
Light armor 10+X+dex bonus
Heavy armor 10+X, stealth penalty, negative dex bonus still applies.
light armor comes with buckler;
+1 AC, you can use your shield hand to fight with weapons, but you lose AC bonus until next turn.
heavy armor comes with default shield.
16. Unify all pets/companions/summons/mounts/familiars to Bonus action command or one attack from Attack action.
17. streamline most spell durations to:
1 round, usually Bonus action cast, and augmentation to your next attack(s) or spell
1 minute, usable for single encounter
1 hr, for local exploration/roleplay/summons/minor area denial (invisibility, fly, spider climb, summon X kind of creature, etc...)
24hrs, for adventuring day (mage armor, darkvision, water breathing, longstrider, various shelters)
18:
bonuses to character level progressions:
1: feat, feat
2: feat
3: +1 ASI
4: feat
5: bonus 2 proficiencies from language, tool, weapon. Skill/expertise is little stronger so that will cost you part of the feat.
6: feat
7: +1 ASI
8: feat
9: bonus 2 proficiencies from language, tool, weapon.
10: feat
11: +1 ASI
12: feat
13: bonus 2 proficiencies from language, tool, weapon.
14: feat
15: +1 ASI
16: feat
17: bonus 2 proficiencies from language, tool, weapon.
18: feat
19: +1 ASI
20: feat
This will ease up on class part of character features, so multi classing dipping will have less effect as less thing will be fixed on class.