I will maintain that the greatest sin of 4e was that it wasn't really learned from.

13th Age is probably my favorite d20 system game, despite some major improvements that 5e has over it, because it remembered to do the whole "let's make the game actually playable" thing.

So many little systems in 4e like the Minions and the Bloodied mechanic (though, honestly, I'm ambivalent about Bloodied) could have made 5e a lot better.

Every time I play 5e, which is fortunately not all that often, I'm reminded of how they stripped away all the combat enhancements.

4e wasn't a great experience in combat (in my fairly limited experience, though that could be a case of my lack of experience leading to a lack of good play), but it really fell apart outside combat.

5e does a little better with non-combat stuff, but its combat is so dull I feel like "accidentally" turning off my wifi while I play online.