I haven't lost a parent permanently, but watching my mum go further and further downhill mentally and physically through alcoholism and manic depression over about five years was like she was dying every day. Plus my Dad had his own problems with drink and low self-esteem. Now that's she's a lot better, I definitely don't take her for granted like I did when I was really little. Both my parents admire me for what I've been through and 'coping' as well as I have, but sometimes I think they don't realise that it has affected me. I don't think I'll ever get over some of the more traumatic experiences (having her brought home by police/being in a car with her drink driving/coming home to a pool of blood, etc) in the same way as I don't think people who lose parents can ever really get over it; plus I don't think you ought to be expected to. Although I think such experiences can mature you, I don't think adults should automatically expect maturity. Sometimes I want to act like a fool to make up for all the times I had to keep it together in order to not go insane, but I'm not allowed to.
I can definitely see where you're coming from when you say you feel different to other people, though. I have a really low tolerance for people who waste their lives: bunking school, turning up late for important things, having little respect, etc, and my friends think I should lighten up. Sometimes really stupid things make me cry and people just think I'm weird. Most of my friends have really stable homes and untarnished hopes and dreams, so sometimes I feel like I'm just the bitter, cynical girl who they can't understand and I can't understand them.
I know it sounds hard, but I guess once you get past the teen years that are tough to begin with without the added trauma of losing a parent like you guys have, people will start to recognise you for the assets you have obtained through going through trauma. Wisdom and maturity aren't things you can get with age.