Our group plays the way our group plays so on one hand, there is very little difference - particularly with
4E borrowing so many concepts from
3E.
However, perhaps the main difference between
4E and
3E for us is that there are more moments where the mechanics of the game and the flavour they represent disconnect and have us go "weird huh, interesting rules glitch there". Most of the time though, we just keep playing, the momentary distraction only being minor.
And actually there is one more thing too in terms of combat. Teamwork is enforced by the rules by having higher hit points and less damage output. No taking the big guy down in one hit or spectacular action any more. As well, since you really want your daily to work, you quickly work out the teamwork to make this happen. Warlord buff goes to Paladin something goes to... my daily just worked real nice. A little mechanical and limiting I suppose but it beats the frustration of mucking up a daily. I'm not too sure if this is a good thing or not.
On the other side of the screen, MUCH less prep required. Monster stats are now completely self-contained. Having monsters and NPCs follow different rules than for PCs is the big design feature here. Makes things a hell of a lot easier to run. In terms of the rules, since the rules borrow so many concepts from
3E, it was much easier to get into than from 2E to
3E.
I suppose that's several differences but heh...
Best Regards
Herremann the Wise