Almost everything in this thread combined. And the same goes for a male lead, really.
- Can be strong
- Can be vulnerable
- Has strengths that they use appropriately
- Has weaknesses that they overcome
- Has intelligence
- Has emotion (not just one of them, either)
- Has a sense of humour
- Has limitations
- Has empathy (personal preference for me on this one)
- Has a past
- Has aspirations
Honestly I don't really care about appearance at all when it comes to writing a good character, but ideally it should be at least somewhat sensible for what they are doing - in other words, if they spend all their time climbing cliff faces, they shouldn't be unhealthily fat, and if they are lifting huge weight, they shouldn't be unhealthily thin. Fantasy/scifi stuff can help get around that, too, though.