The games are pretty much true re-releases of the classic titles which means absolutely nothing has been touched. The only additions are core Nintendo emulation features which include online battles and trading with other players, so no need to find the old cords!
The trailer includes footage from all 3 games including Pokemon Yellow which has a bit more color added to it, and of course the fact you get paired up with Pikachu instead of your choice from 3 pokemon characters.
Also worth noting is a little tid bit at the very end of the trailer. It seems Mew has been unlocked for all 3 games! During original releases Mew was more of a myth only being unlocked via Nintendo events or through glitches.
All 3 titles will release February 27th.