4e broke plenty of rules, vansen spellcasting probably being the biggest. But it's the only serious attempt to making a remotely balanced version of D&D and character portal-able version of D&D, concept that D&D struggled with from day 1, and have been utterly ignored in 5th. I went back and watched Matthew Colville's making a fighter in every edition of D&D. To me looking at the progression D&D from tactical war game to modern RPG, 4th hit closest to home in terms of logic progression. It pulled concepts developed the in the MMO industry into the table top parlins, it codified a lot of concepts. Skill challenges, Power Sources, Monster Types (Lurkers, Brutes, Soldiers, Artillery), Defined named party Roles (Strikers, Tanks, Leaders, Controllers), it redefined the save vs Death Mechanic into an acceptable modern form, it redefined adventure construction encounters, skill challenges, combo-challenges, shorts rests, long rests, downtime activities. The creation of healing surges lead to develop expending hit dice for recovery, defined DPR, it reversed so much of what defined negatively in the past editions into positives (-2 or -3 if you didn't proficiency become a bonus if you did). The concepts or ritual magic, magic item creation, codified magic item progression and usage were all well defined and level linked to enforce some level balance. Play tiers, and scaling economies based upon those tiers (See gold coin, Platinum coins and astral diamonds). It was aggressively updated, with codified with living errata documents and a system for purposing changes. It created a structure for increased drama in an encounter with introduction of the bloody mechanic, and creating triggers that were activated by that mechanic. Finally it gave D&D the easiest encounter adventure construction method to date. Making 4th adventure was as hard falling off a log, there a literally a button you could press on the online tool that would do for you, complete with everything.
It failed in a couple key places. One the online table top. Right from the beginning 4th was always intended to be paired with an online way of Running 4th a means to help players be able to solve the distance and time issues. That failure and that fact that it was never correct b/c some poor sod killed his wife and ate .45 is a truly tragic, both for them and game itself. Next 4th was never very good at helping the player imagine the other half the ability. How does the power look? Does look for each character? Do you recognize this power when your character sees it? those meta concepts general well defined in Pathfinder didn't carry well into 4th. Finally mechanically the stun and daze mechanics were too common, and trivialized combat.
5th is simple and there is beauty in simplicity, we are getting to there point where there enough diversity to begin to make interesting. I agree it can feel kind dumbed down at times. But it's well written. It's not being aggressively expanded, which is keeping power creep pretty locked down. They did learn many good lessons from 4th, and they did a better job of selling to the player base. It's feels a lot like AD&D 2nd Rev which was certainly the intent. I don't like it as much 4th. A third level 5th character is as complete a character as a 1st level 4th character, and the DMG does recommend beginning at 3rd level in 5th. But there you go, that's also working as intended.
