First would be to help people. Field medic, builder, that sort of thing. Second is traveling the world. And the third? Piloting a fighter jet. Problem is, I'm too tall. At 6'7", my head sticks about a foot out of the cockpit, and I really don't think they make convertible jets.
Another appealing aspect is the brotherly bond that many soldiers feel. Having someone you trust with your life working with you.
I really don't plan on ever joining the military, as I can do pretty much all of that as a civilian. I can see why some people find it appealing though. Many do it for the supposed adventure, or the honor, or the order. Are they right? I don't think any of us can really say.