The Ending (spoilers)
Swanson spent most of the movie completely detached and seemingly unfeeling. He didn't really seem to get much joy (or any emotion) from almost anything except maybe at the expense of others. He just sips his drink as a woman has a seizure in front of him. He's pretty much a sociopath. But at the end he's on the beach with a little boy, playing in the water and he seems to be having a lot of fun. Because that's all he really is, just a boy. A 35 year old a-hole kid. I said he's pretty much a sociopath but his energy and the fun he has in that scene kind of stands out as a ray of hope for him. That he can feel. That he can enjoy life. I thought the scene was very poignant.
Also, I doubt it was intentional but the line Eric says in the cab is to me, kind of like a thesis statement about the film - or at least about Swanson (who is the film.) "You're just a wooden boy." That pretty much sums him up. Wooden, soulless. Aching for life but not really getting it.