As of last night, I’m in a position to judge D&D 4th Edition based on something other than hearsay – since I have now played some. That said, I haven’t played much so I only have a keyhole view of things.
The introductory session involved rather a lot of combat. As usual with D&D, combat took up most of the session. It was, however, rather more interesting then first level combat in 3.5. Everybody got to do something active each round so there was none of the old “I hide (having expended by one offensive spell of the day)”, and given a choice of attacks the fighter got to do something slightly more interesting than “I hit him with an axe”.
So, combat is, in my opinion, rather better at low levels.
Roleplaying? No problems there, the system didn’t get in the way (or appear to cover it for that matter, skill checks were limited to knowledge rolls).
The one bit that I’m really iffy with is dealing with challenges posed by the environment or traps. I’m sure they could still be dealt with by ingenious use of mundane items, but my impression so far is that magic and skills won’t help matters at all. This, however, is still based on theories formed from glancing through the rules. We’ll have to see what happens when we get actual problems to solve (and I’ll hopefully be able to have a proper look through the rulebook at some point).