Characters should have enough good points to make you sympathize with them (or at least understand why they are the way they are in the case of villains). Everything about a character should make sense for that character. (Even crazy characters have reasons for being that way and showing those reasons will help foster sympathy for that character).
Characters with a good sense of humour go down well, as do characters who can recognize their own failings and recognize where they need to improve.
Characters should have their own distinct voice. My Eileen is crisp, clear and blunt. The latter trait of course lands her in it time and time again, also can cause problems for her with regard to her daughter, Jenny, who is as blunt back again.