Keith Baker, creator of Eberron, compares 4E to World of Warcraft and MMORPGs on his blog. He has design experience with both so he has some insight.
Jason Buhlman, from Paizo Publishing, gave some criticism of combat in 4E in an Enworld interview. The first real criticism I've seen:
Jason contended that the new edition's apparent focus on adding variety to player options and keeping people engaged at the table at all times had seemed to him, after 2 preview sessions, to be a "partial success." While the "Encounter" and "Daily" powers on the sheet were interesting, it seemed like PCs were once more reduced to "doing the same thing over and over again" after they had burned through them, something that the 4e designers had at least ostensibly attempted to avoid. He confirmed that, in one of the previews he played, a final combat had lasted for nearly 40 rounds(!) (apparently against the 280 hit point Black Dragon mentioned elsewhere).
Finally, one of the D&D Experience participants, Mike Shea, was able to reconstruct the second adventure that was played. He posted it here. So we've got sample characters now and a full adventure.
The D&D Insider interview on Enworld revealed a few details that I think are wrong with the product. These are all things that have been done for business reasons. First, you have to purchase the electronic miniatures beyond a base set. This might makes sense with a stand alone, retail product, but with a subscription service, this kind of stuff should come for free. If they really want to go this route, they should print codes on the D&D miniature products that allow use in Insider. Second, you can't do any of your own 3D modeling and custom import stuff. They were surprised that they had so many requests for this. Third, and most importantly, you can't print your fancy maps, since it would compete with their Dungeon Tile products. I'm not about to create a fancy map so that guy across the country can play with us, but not have the same map available to my players in front of me. I'm hoping they go back home with some clearer ideas on how players intend to use this thing.