The main problem with 3.X was that there were some options that were deliberately designed to be better or worse than others with this concept of "System Mastery". So some concepts were put in as deliberate traps. And it got tiring after a while. 4e I'm given to understand was a lot better and more stable after a bit and it continued on a lot after I gave up on it, and it introduced a lot of cool things, but it didn't really have the same flavor as D&D.
There's a clear progression from Non-Weapon Proficiencies to Skills in 3rd Ed, deciding that 3rd ed skill points were a bit much and moving to the way skills work in 4th ed which got carried over to 5th ed.
1st ed had a lot of variant classes in Dragon magazine et al and then became kits in late 2nd ed. 3rd ed had the idea that of building up into Prestige Classes rather than starting with a Kit, an idea that continued a bit into 4th ed which had built in prestige and epic destinies.
5th Ed is sort of mixture of 2nd ed kits and 4th ed prestige classes being built into the class.
Multiclassing/Dual-Classing in 1st and 2nd ed was a bit bleh and weirdly dismissive of folkloric or fictional characters that were often a bit all over the place.
3rd edition multiclassing was an excellent idea but not well implemented and you could mess yourself up badly if you weren't careful
4th ed multiclassing I didn't really like, it felt a bit "well, this was in prior editions"
5th ed multiclassing has the basic structure of 3rd ed multiclassing but makes it a lot harder to accidental handicap yourself due to the things that advance based on character level (cantrips, spell save DC, skills, attack bonuses, etc) rather than class level. However, the subclasses mean you don't really need to multiclass very often, so it's sort of a "if your story goes this way, it's an option, and it won't really hurt you overall". I currently have exactly one multiclass character and that's a bard who read the Book of Exalted Deeds and became a celestial warlock as a result. The story just felt right.
1st and 2nd ed level limits are things am very glad to see go and I'm happy to see Ability Score bonuses being less associated with species though I'd prefer them to have been associated more explicitly with backgrounds and classes rather than just being vaguely "pick a +2 and +1" but you can do that they they've done Tasha's.
I initially loved 3rd ed races, but got a bit less enamored as it became clear how inconsistent they were in capability. 4th ed was interesting and I was happy they decided to make humans something more than just "the do-anything race".
The way 5th ed is going for race packages being physical capabilities and culture/upbringing related stuff being more flexible is neat. I do think some races are designed a bit too close to MM stat blocks (Yuan-ti for example has abilities that are both boring and a bit much for a race package despite being a race that has some lore I really want to play... there's some stuff in yuan-ti that neurodivergent me relates to a lot and defector from decadence is fun.) I like the idea of giving players the option to get a lot of flavor out of myths (demi-gods and half-demons appear a lot in myth and folklore and we have tieflings, genasi, and aasimar for that) but I'd like race stats to be more mild... for really powerful species I look to classes... for example sorcerer is basically "species/mutation as a class". And it would be nice to see a for more things like that for other classes (granted some of the psionic subclasses are good for this too... and I've fluffed a four-element monk as a progressive mutation rather than a product of training.)
Feats....
I would like to see more... 5th I think REALLY underestimated how much personality Feats can give a character and how much the process of leveling up a character can help get into the mind-frame of your character's developing personality and history. I know a lot of the fun of leveling a character is gone for me when it becomes a "adjust numbers" rubber stamp and it's a bit harder for me to visualize a character's story arc as well when a level-up lacks unique personality.
