I love how nonchalant he is. He seems so easy going and happy. Off the top of my head I can't really think any songs that he sings that are heartbreaking or sad. When I listen to him sing I can't help but smile and dance, he just seems so darn happy!
You should probably just listen for yourself:
This one might be my favorite:
And here is a playlist of some of my favorites, just click on the link. Dean Martin Favorites