Having to chmod my samba shares to 0777 feels wrong just to get them to be writeable. Is this really necessary?

Since setting up my samba shares I have been unable to write to either of them. My config:

[minecraft]         path = /opt/minecraft         writeable = yes         browseable = yes         read only = no         guest ok = yes         create mask = 0777  [www]         path = /var/www         writeable = yes         read only = no         browseable = yes         guest ok = yes         create mask = 0777 

I am unable however to write to either of these shares from a Windows machine. I have the folders themselves (and all subfolders) at 755, but still nothing.

The only thing that has allowed me to get the shares to be writeable is making them and their subfolders 777 and that just feels wrong.

Am I missing something?