There are many ways to describe people using Chinese.  Some ways use 4-character idioms, and in other cases you can simply use 2-word phrases.  Here are a couple of my favorites which I have encountered during my time thus far in China.  A person who doesn’t keep promises very well is referred to as being 不靠谱.  A person who is somewhat restrained in public company is referred to as 收敛.  A conservative person is referred to as being 保守， whereas a more open or liberal person is referred to as being 开放.  However, it is possible to become too open and freewheeling- a person like this is usually referred to as being 随便.  A person who is able to tell how to treat people is said to 有心眼.  Finally, a person who is very closed-off to the world and has very limited social contact is said to be 自闭.  If you know this word, then you can also describe a person with 自闭症(autism).

收敛 shou1lian3 - restrained in public, reserved.
靠谱 kao4pu3 - keeping promises.
保守 bao2shou3 - conservative
开放 kai1fang4 - liberal
随便 sui2bian4 - freewheeling, careless
有心眼 you3xin1yan3 - able to read how to treat people
自闭 zi4bi4 - closed-off, shut off from the world
自闭症 zi4bi4zheng4 - autism