“What makes for a good character?”
A good character is a character you enjoy playing. Tautological and useless, sure, but hat’s my best answer.
What makes a character enjoyable to play is going to vary for everyone. Namely, it’s a character that allows then to pursue their agenda at the table, be it kewl powerz or dramatic anguish.
For me, it’s a compelling hook that makes me want to learn more about the character, as well as some role or ability that I look forward to seeing them pursue in play. For example, I’ve had a character for an upcoming Burning Wheel* campaign banging around my head for a few weeks now. She’s an amalgam of some fantasy tropes that I enjoy, some characters from books I’ve read and films I’ve seen, and some particulars of the rules that I want to bring into play. I’m already picturing some of the things she might do, some of that tasks she may have to accomplish, and hurdles she’ll hope to overcome. I have yet to touch pencil to paper, but I’m already looking forward to playing to find out what happens to her.
To go into more depth would require, IMO, focusing on a specific RPG.
* Ha! You thought I’d make it through one dang RPGaDay post whiteout mentioning BW. Suck it, h4t0rz!