Derek's elevator proposal marks a relatively bright spot in an otherwise sad and complicated episode where we see Cristina grapple with Owen's PTSD and Izzie and Alex confront the possibility of Izzie's death. Richard proves to be a pretty great wingman, refusing to move until Meredith hops onto Derek's elevator, which is decked out with all of the cases that he and Mer worked on together.
While brain scans aren't as picturesque as candles, it's exceedingly difficult not to cry when you hear Derek propose to Meredith. Derek tells Meredith that her "dark and twisty" tendency isn't a flaw — it's a strength.