There are lots of 'symptoms' that are great about being an entrepreneur, but I think they are all a result of Self-Actualization (and maybe Self-Transcendence) from Maslow's Hierarchy of Needs: http://en.wikipedia.org/wiki/Maslow's_hierarchy_of_needs
For me, this manifests as:
* Creating change for the world outside of personal gain.
* Learning the limits of what I can and can't do. Nothing like jumping in the deep end to learn how to swim.
* Getting fulfillment that I wouldn't get elsewhere. E.g. amazing people, satisfaction in work, creativity, and bringing meaning where there would be none.
There are some commonly cited but wrong answers. It's highly unlikely you "have no boss" as an entrepreneur (fiduciary responsibility to shareholders). You don't get to do whatever you want. You don't get to slack off and take vacations.
There's also the "E-Myth" - if you like baking pies, don't open a pie bakery, because you'll spend barely any time making pies and you might come to hate it.
I believe some people are meant to be entrepreneurs. In other words, just like how you don't choose to be gay, you don't choose to be an entrepreneur. So the best thing about having an entrepreneurial job is that it lets you be who you truly are.
... or as I put in some of my social profiles: "I learn by pushing boundaries until something pushes back. So I landed in one of the few jobs that rewards such silly behavior ;)"
There are many benefits, but for me it is the truest expression of myself. I can take the long view and set myself on a path of learning and growth that allows me to accomplish the change I want to see in the world. It allows me to express my personal core values through my business activities. But the best part? I don't have anyone telling me during an annual review that I "could be less ambitious." Good riddance.
If I'm choosing something that is unique to entrepreneurship, I'd say the flexible lifestyle. I had my choices of work I love to do without owning a small business, so it's not just loving my work, though I do.
And it's not the unlimited income potential. You can't eat potential, and you can have the same potential if you go into outside sales.
For me, it's going to movies on Tuesday mornings, then working for the rest of the day. It's being able to take vacations in the middle of the week while colleagues are at work, then return just in time to join friends and peers for a Friday night drink.
It's not just knowing I can work from anywhere, but actually Doing it, packing my laptop and three days of clothes and just leaving, with no particular plan.
It took a couple of years of working 18 to 20 hour days to get to this stage, but it's wonderful to have these options.