Now that the movie is out I can get a better analysis of BB-8. This will be quick, because we already knew so much about the droid. Let's break it down:
The head spin isn't what I thought it was. There was some talk about how the head spinned, but we were all so focussed on the BB-8 from the Anaheim Star Wars Celebration in which the head spins on top of the body. In the movie the head actually spins on top of the metallic rim on the lower part of the head. It's not a complicated thing to do in a real-world BB-8, but it would add substantial weight which is probably why the stage BB-8 did not spin that way. Others are saying it's just to keep the head from falling off.
The sound effects are not what we originally heard when the Star Wars celebrations were going on. Abrams must have changed the sound effects later on while the film was in editing, but I really don't know why. The sound effects have a bit less reverb and are much more muffled. I'll need to find some sources to extract the new sounds for my BB-8.
The circular light on the head to the left of the holo projector (small and white) actually blinks to show the droid's mood. It does not always blink when BB-8 speaks, but sometimes it does synchronize with his speech. The rectangular white light to the left of that circular light is not always on. Also as far as I could tell I only ever saw one red light on the head and there were not multiple lights in a line with it that ever came on. I might be wrong there. It's possible in future episodes we might see the eye show more lights, but I did not see that in The Force Awakens.
My review of the movie? It gave me a real feel of Star Wars as it was from the original trilogy. The practical effects and film really helped that. I think Abrams achieved what we wanted more so than he did in Star Trek and I feel very satisfied!