I thought it was beautifully done. She heard and felt the love that her family was trying to convey to her in her final hours/minutes, and it gave her the peace to pass on. I was with my dad when he died, and II like to believe that he felt that too, and that just maybe the hand squeeze that I felt was him taking my Nana's hand as she guided him to Heaven.
They did spend too much time on Marcus and his family, but I think the point of it was to show the irony that the early clinical trial of Marcus's Alzheimer's drug was probably the one that Randall wanted Rebecca to join and may have helped her.