And I don't think Mike should be singled out here. I never got the impression that WotC fully understood exactly what they created and how it should best be used.
Yeah, I don't pretend to know what all the other devs thought or understood either. I mean, its not like H1 (KotS) is the only module that doesn't exactly shine. Honestly I have not even read the others in the HPE series, but my impression from what I read about them is that, at best, a couple of them are mediocre. Later modules definitely improved, and there were some Dungeon adventures that looked reasonable (I only really ran one of them, and it wasn't great, but a few others have been considered good). The modules released in the later period seem to have learned some lessons.
So, yeah, probably there were issues, though the guys who wrote the DMG1 and Kobold Hall, etc. seemed to at least partly get it. I mean, DMG1 has some pretty solid narrativist type stuff in it.
Adventure design is one the ways this shows. Although later adventures were slightly better than KotS, none of WotC ones really took a Zeitgeist like design of one big map story important combat in between lots of other stuff (exploration, free roleplay, investigation, etc.) which was probably 4e's sweet spot. Or spread out the right amount of XP into multiple rooms that were expected to converge so it turned into one big regular encounter.
What I found to be missing was dynamism. When I make a 4e encounter something is on fire, exploding, collapsing, running out of control, etc. Never make a static 4e battlefield! This is the game where you pretend you are Spielberg and go wild. If you wouldn't see it in Jurassic Park or Raiders of the Lost Ark, then it don't belong in 4e!
Rituals were also almost completely ignored in adventures. (and in the system in general). Imagine if
1) rituals were split into Arcane, Divine, Primal and you only got access to one list with your class (or the feat)
2) traditional full spellcasters like Wizard, Cleric, etc. got a few free Ritual casts a day and that was put into the class description in a Spells Per Day type chart. Say eventually One per day at Level -1, 2 per day at Level -2, and 3 per day at Level -3 or whatever. And got 1 free ritual added to their ritual book per level.
3) adventures assumed you might have access to some of these and enemies use them too
Rituals were such an amazing answer to "how can we have this kind of powerful utility magic that D&D is known for and not have it be tied to certain classes or too often circumvent combat encounters?". Then they completely ignored it, taking away a big part of the "feel" of prior D&D.
They aren't totally ignored, but the parcel treasure system makes players feel like they're getting ripped off when they pay the costs. Its an unfortunate psychological mis-design of 4e. Probably not something you would see until you got it out there and played a bunch, but anything with a GP cost suffers from neglect.
Being so wishy washy on explaining some of the effect first mechanics and how that works, etc. Just lay it out -- HP are not meat points, prone is a condition that represents hampering an enemy and usually that can be represented as knocked to the ground but could also...
Well, they did do that, but you aren't going to win over the usual posters on EW with that I'm afraid.
I find the "creativity/imagination" comment from above very funny, because I found 4e played much much better with players that were creative and imaginative. The kind of players that could make skill challenges work well by reacting to the fiction in a push/pull way, could help wrap a narrative around the occasional mechanics where the default narrative didn't fit perfectly, didn't have a problem using improvised actions which I could easily make worth it using p.42, never thought warlords were shouting wounds closed because they were imaginative enough to think of HPs as partly a narrative device, etc.
I thought it ENCOURAGED people to be those sorts of players. I mean, I had 4e players that just wanted tactics, and ones that just wanted to go along for the ride and not contribute much or try very hard, but EVEN THOSE people 'got it'. The two I'm thinking of did both eventually drop (one got pissed because the other players weren't optimizers, and the other just had too much else going on to keep playing). So, yeah, it didn't 100% grip everyone. OTOH I did see pretty positive results with 4e getting people's creative juices flowing. I could probably do as well with other games I like running, but it was solid.