My favorite thing about the movie is how well it combines humor, sarcasm, and sweetness.
My favorite thing about David and Elizabeth is how at the beginning of the movie they both have issues and they can't stand each other, but in the end they come together and it all works out.
Favorite thing about the actors themselves... Well Reese seems to be a genuinely nice lady and I respect that. As for Mark, I just adore him. He is one of my favorite actors and some of his performances (like in You Can Count on Me) are nothing short of amazing.
There are lots of great things about the supporting cast; they really add a lot to the movie, especially Darryl and J.J. They have some of the best lines in the movie. They are both quirky and a little neurotic, which makes them even funnier.
"You are named for the dog??!!" - Sallah, Indiana Jones
I love this film, it's not a great work of art, but somehow it does work. There are a few plotholes to me (like why do they let him just walk away after basically trying to steal her body in the hospital?) But I love it because of the two main characters mainly. mark R plays the morose sarcastic man so well. And then the way he changes and falls in love with her is so well done, so real, compared with many romcoms. The loneliness of both characters, in different ways, is so tangible. There is an other worldliness and steaminess about the film. Although the premise is completely crazy, it just works somehow! The fact they can't even touch adds this poignancy. It's also very funny and sweet, as others have said. And basically I love mark ruffalo!
Agree with everything you said about the film, although I swing more towards Reese Witherspoon as I love her work and the woman herself is simply gorgeous...