ADvantages include better gas mileage( 20-30% better than gas), no additives like gas (ethanol) and much better torque than gas. Honda says that their diesel will comply with Cali's strict requirements. It's my hope that diesel makes hybrids obsolete.
All I remember about the Olds Cutlass diesel I bought from my folks in 1983 was that is was useless in Detroit in January unless I could garage it or park near an electrical outlet. Is climate still an issue with the current generation of diesels?
I do remember that it was otherwise largely maintenance free as long as you changed the oil regularly.
It takes more oil to make a gallon of diesel than a gallon of gasoline. Per pound diesel and gasoline have about the same amount of energy. It's just that diesel is a heavier fraction of oil and is denser. It would be foolish to use MPG as a basis for comparing diesel and gasoline vehicles.