On Sunday afternoon I ran my first 4e game—part of an adventure I call The Malevolent Mystery of Marshburg. The session went pretty well, particularly in light of how long it's been since I've written an adventure or DM'd, and that none of us have played 4e. My players even asked if we could continue the adventure tomorrow after work, which was a nice complement.
In five hours we gathered rumors in town, found the dungeon site, explored a half dozen rooms, and completed two major encounters. Kobolds were defeated. A trap was disarmed. One PC was reduced to zero hit points, but recovered. All but one of the Goblins were killed, and that one managed to escape by spiking a door shut between him and the PC's. (If the players can do, why not the monsters?)
I tried to run certain aspects of the game in "classic mode". The trap was disarmed through dialogue between me and the players rather than a simple role, for example.
4e feels more like a tactical miniatures game than any previous edition, but that's all I'm prepared to say until we give the game a fair run-through in a number of sessions.