The major difference between their lives is that the United States is not in a truly large war today. Soldiers today might be deployed to Afghanistan, but they stay for a limited amount of time and are not in a full-scale war the whole time. Soldiers in WWII were in for "the duration" and the war was a full-scale war rather than the anti-insurgency operation that is going on in Afghanistan today.
When soldiers are deployed overseas, the difference is huge, largely because of technology. A soldier in WWII might get letters, but a soldier today can be constantly in touch with his or her family. Some of my ex-students are or have been deployed to Afghanistan or Iraq and are still able to communicate with family and friends in many ways, including Facebook.
The life of a soldier in modern times is easier given that we are not in a full-scale war and given that soldiers who are deployed overseas can feel less isolated from their families than they once did.
Many of the soldiers in World War II were draftees. Now all military personnel are volunteers.
Soldiers received very small pay in World War II, something like $36 a month for privates. Few could afford to get married. Now career soldiers can marry and have families.
Soldiers and sailors during World War II had to wear their uniforms at all times, on or off the base. Now they can and do wear civvies when off duty.
Soldiers have much better transportation now. They receive better medical care and better prosthetics if wounded. Wounded soldiers have a much better chance of surviving because of miracle drugs and generally better medical attention.
The military has become much more technologically oriented. Therefore, soldiers get much more technical training, which is a big asset when they return to civilian life.
It should be pointed out that most soldiers used to be men. Now there are many women in the armed forces, and they are no longer segregated as WACS, WAVES, etc.
Soldiers now have much better weapons, including their semi-automatic rifles, which are far superior to the rifles men carried in World War II.