Kaiyanwang
Adventurer
And power, specialisation, skill, and ritual (where relevant) choices make it possible to roll members of any class in 4e that are dramatically different from one another.
You are pretty absolutist in your statements

You mean the large clunky thing that meant that with preparation time Wizards could do anything?
I mean the large clunky thing tham mad the wizard feel like a scholar. And what you adress is a spell mechanics problem, not a spellbook mechanic problem. This is just another "baby with the bathwater" problem.
As a PC I do not expect to have a clue how dragons cast spells. And in some worlds they become less magical if I do things the same way. As for receiving spells, that was cut-scene background flavour text in my experience.
As a 1st level PC? Sure. As a 20 level sorcerer that just dicovereed something on his ancestors? And has 23 ranks in Knowledge (Arcana)? See how all these things just SCREAM inspiring backstory?
Cut scene background? Divine spelcasters received spells in specific moments of the day (say, good clerics are said to receive spell at dawn and so on). This could influence the whole adventure!
And 4e is one hell of a lot better at the mechanics interacting with the game world at a local level. Pushes, shifts, slides, marks. Those things matter at a local and immediate level. "Casts spells like a dragon" is an abstract. "Slips through the combat like an eel, avoiding opportunity attacks" or "drives the enemy backwards" is concrete.
All these things were present in former edition, just without prepackaged rules. Did you ever tumbled to backstab playing a Rogue? Or beaten a enemy with Standstill playing a fighter? Or cast a repel metal playing a druid?
Now you have automatic "shift and hit" without a tumble check + hit roll, or a 6[w] without the need of a critical hit (but HP raised up to the wazoo, so a good old crit with a greataxe remains far more satisfying).
"Cast like a dragon" is non abstract. And my imagination is not stroke and stimulated only by things inherent combat - quite the opposite. I alway built interesting combats only with core skills and maneuvers, splats just added to it. I like interesting tools for combat, but just handwave the rest... is quite dismissive design.
OK. I'll grant 4th. (I forgot about the Animal Companion). But other than archers that's less variety than is in 4e fighters. (4e Ranger might be a better fit.) Even smite evil is a 1/day stronger attack. A pretty generic Daily (and the spellcasting's just utilities or rituals).
You are completely overlooking the ranger skills, wild empathy and track. If they are out of combat (maybe) things, does not mean that are not interesting. " Archer" is not trivial. Rituals... do you honestly think that can be used with the same frequency and reliability of detect poison, bless weapon, animal messenger, longstrider?
The classes actually were far more bland at level 1, but had the chance of differ a lot later. And were simpler AT LEVEL 1 to play for a newb.. just to remain in the theme of Essentials

What stimulates my imagination isn't what's on the long and complex character sheet. It's what they do. How they act. And at this micro level, At Will powers kick the arse of 3e.
My examples about time for clerical prayers for spell didn't made the sheet more commplicated. Just the gameworld more interesting. IIRC, we discussed about it previously, and I remain of the opinion that the 3rd edition at wills (feats) are simple and dull in the beginning, but when you start to combine them with other ones (fighter mostly, but everybody) or with class features (paladin, ranger, barbarian, rogue) are far more satisfying.
This does not mean that some thing could be done better (mainly, in the way they scale) but this is another matter.
In the running the gameworld? Agreed. 4e makes no attempt to be simulationist.
Is not even a matter of simulationism. Is a matter of inspiration. if things are uninspiring, seem same-y.
The Bard is now popular? Rather than the red-headed step child of 3e? (I used to like it. But always thought that was a minority opinion). And as for errata, any game needs it.
People tend to compare classes on raw numbers. I've seen it even in Pathfinder thread elsewhere.. "But Barbarian does not deals as much damages as the fighter at level 20! It suxx!1!!!!1". Ignoring the d12 + uncanny dodge, or things like a raw +20 on strenght checks each rage (or each round, just to be sure to take the Balor from the neck).
Barring the fact that the base CONCEPT of the bard is a blast if played by the right player, once you understood that you role is a face -support -jack of all trades, you love it. You want to pew pew? go sorcerer. Don't play a bard like a sorcerer. don't play a monk like a fighter. Better don't play a fighter like a fighter, sometimes!

As a side note, splatbooks added a lot of love for bards.
ERRATA: Any game needs it. Of course. Even better if you make it a continuous process, making books obsolete and a subscription to an updated charachter builder mandatory..