Balance in life?
Financial security, independence, etc?
Lot's of free time while keeping the bills paid?
Pursuit of long-lived dreams/goals?
Positive contributions to society?
Lots of opportunity for creative expression?
Accept the past. Live for the present. Look forward to the future. Robot Fusion
"As our island of knowledge grows, so does the shore of our ignorance." John Wheeler
"[A] scientist looking at nonscientific problems is just as dumb as the next guy." Richard Feynman
"[P]etabytes of  data is not the same thing as understanding emergent mechanisms and structures." Jim Crutchfield
Success for me is finding the good fights and getting into them. It is discovering and working toward the causes which I am willing to die for even if I have no hope of achieving any of them in my lifetime.
Success means being at peace with decision and not feeling like there's something else I should be doing, primarily. After that, interest in what I'm doing, ability to cover expenses, ability to help people, ability to feel proud. Maybe these are just the sufficient conditions for the primary requirement, or maybe just the necessary ones.
Hmm, interesting question. Contributing something useful to society is probably a major part of it for me. On a more mundane level, a secure job that gives me some financial freedom is also part of it.
Success to me:
1. Being the lead or subject matter expert. Shallow I know but it is what I strive for.
2. Being able to manage your own time.
3. Maybe should have been first but financial stability. I don't think I will ever make millions in what I do but I enjoy it and really would just consider success being if I can live comfortably.
Career-wise, I'll be happy when I find a job that:
-pays well enough to keep me comfortable
-is stable enough that I'm not stressed about it
-is variable enough that I don't get bored
-is intellectually challenging/interesting enough that I don't get bored
It's also important to me that my actions will be meaningful to someone and that my work will go to accomplish something, but that's less under my control. It would also be nice to have a boss that gives me desired outcomes and lets me achieve them however I want, but again, that's not really under my control.