Presentation- period- was 4e's downfall, It was never presented well at all. In the way they split the info up, the aesthetic, the marketing, and most importantly, it's presentation as combat as sole focus in rulebooks and adventures. This was an issue for core and Essentials,
I'm with you though- I love Essentials- and it' s my favorite WOTC version of the D&D game (I grudgingly give 5E the "best" iteration- as it is not terribly polarizing, is a smooth running game at the table without too many kinks and can accommodate casual players well).
I guess I'm out of step, but I though the presentation of Essentials was the best I've seen for an RPG. I didn't have any thought of playing 4E until I came across the Essentials books at my FLGS. Flipping through them, I could look at a stat block and understand what the PC or Monster could do without even knowing the system. Instead of walls of text, I was looking at game information displayed in a clear and intuitive fashion. I finally had, in my hands, an RPG that I knew would be easy to run at the table.
And I love the digest format. The only reason we still present RPG books in 8 1/2" x 11" hardcover format with walls of text in 7.5 pt fonts is legacy. If tabletop RPGs were invented today, there's zero chance they're be delivered in that format. 5E was a huge step back in book design, defying all modern layout and design principles out of, presumably, a goal of feeling familiar rather than being effective at conveying complex information.
Digest format books are light, easy to flip through and reference, easy to pass around and share. And presented with the reasonable font size and spacing between lines in Essentials, easier to read than the walls of tiny text in most RPG books.
Then there's the excellent Rules Compendium, with all the mechanics for the game summarized in a portable handbook you can fit in one hand - such an obvious innovation it's baffling nobody thought of it before.
I'm in the writing business, and I've GMed for over 35 years. The D&D Essentials books were the first RPG books I've seen that were clearly produced by instructional design and layout professionals, and not hobbyists who took a Adobe Publisher course.