This was the video shown at TGS.
Pretty much explains itself.
Still awesome though,
All units from the first game at this point are pretty much confirmed for return.
New units (note new doesn't mean playable) from the PV
Turn X Gundam (YES!)
Dark/Devil Gundam (DG Heads everywhere)
Official Mode seems to cover the events of UC more in depth (like how almost everyone Kamille likes dies)
The Mission Mode seems to cover what Original Mode did in the first game.