I've delayed writing because of a week of sad and busy circumstances, but here it is, my assessment of D&D 4th edition, based on the game I ran last Saturday.
A caveat: the party consisted of two PCs played by Scott and one played by me, when calculations for XP and opponent size are based on a party of five. That made it a little more challenging up front for planning encounters than it should've been. I did make use of the online encounter builder at the Wizards site (I'd link to it, but I don't think it's free anymore).
I heavily modded Keep on the Shadowfell. In fact, not so much of the "keep" nor the "shadowfell." I made much use of a series of articles by Justin Alexander from the Wizards forums. Just a note about KotS–the proofing is awful. On one page I found differences in stat blocks that obviously reflected a change in how they intended to regard ability modifiers.
Combat took longer than I expected. The DMG indicated 1 1/2 hours for combat, which I thought must be grossly overestimated, but it wasn't. Granted, we had a learning curve to overcome, but we easily took an hour and then some to defeat 6 kobolds (4 of which were minions). I do like the minions rule–one hit and they're dead–but you do still have to hit them, as Scott said. The powers were interesting and did give you the ability to do something every turn, but that did often end up being the same thing over and over, not that much different than in 3.5.
After rescuing the dwarf father and son beset by kobolds, the party moved on to town to try to meet their objective of locating the heir they'd been sent to find. Scott's characterizations were great, as usual, especially the lawful good Cleric of Eratis with a foul mouth and a hatred for anything not a city. She was a lot of fun. I probably should have used some skill challenges here, but in planning I focused more on combat and the story, in typical Donna fashion.
Naturally investigation was interrupted by danger. Undead were roaming in the graveyard, so the heroes ran off to fight some skeletons and a couple of 3rd level gravehounds that gave them fits. Killing the gravehounds took forever.
They went down into the mausoleum of the follower of Bahamut and found the sacrificed woman. Next stop–room full o' skeletons. They were all minions, contrary to what I had originally intended, and again took forever to kill. They didn't get to the cool encounter with the ghostly paladin, nor save the day in their final battle with the UBG (well, low level UBG anyhow). So close, but that would've required probably another couple of hours to complete.
All in all, I have to say, <shrug> Eh. I wasn't overwhelmed by the Great Fun of It. Combat does go smoothly for DMs, I have to say, but I've been running games for a long while. Prep work was more time consuming than I'd been led to believe. I should have included some traps or other cool displays of 4e, but the sections in the DMG seemed complicated and I didn't read them. Truth to tell, I ran out of time.
I'm glad we played, and I wouldn't be opposed to playing again, but if we don't, now I don't feel I've missed out on anything. I guess the bottom line is, I don't see what all the fuss is about.