Having worked on it a few times now, I can say, that it's a 747. Not that different from the 200/400 series I've worked on for years now.
As far as noting more movement in the back, my experience is that it's the same as on the 400. To me it doesn't feel different at all.
I also noted the mentioned lack of noise and "thumping" when the gear goes down, which I miss, as it's a convenient " last call" to get to your seat for landing.
Other than that, there are not that many differences inside the cabin. Intercoms have been upgraded,and have displays now, the IFE can be reset from the Galley, and finally the cabin temperature can be managed without having to bother the Purser (which is airline specific though, I believe) and also new to me is the liquids disposal unit. Nice touch, that.
Lighting options have thankfully improved, overhead bins have more capacity (not sure I should be mentioning that), but are more difficult to close.
Crew Rest Area has been relocated, and is now even nicer than on the 400. This though, I was told by a Boeing Tech, came about not as a perk for us, but happened as a consequence of moving it. Still very much appreciated, of course.
So, basically, everyone that's flown on a previous version of the 747, will be right at home. It's still a 747, but a much nicer one.
Oh, and the crappy door 5 is still the crappy door 5.
Everybody who's ever had to close that door, hanging out of the aircraft with wind, and no stairs beneath oneself (yes, ocasionally that does happen) will know what I'm talking about.