I've seen it before and there was much disagreement as to whether the dog was having fun, or not.
I try not to jump to conclusions but it looks chilled and relaxed. One of my dogs would have loved having a bath like that and the other would have gone into a total panic at the prospect of water getting near him.
Certainly looks relaxed to me. He closes his eyes for a spell on a couple of occasions, as if he's about to fall asleep. If he were fretting in any way he would be quite agitated.