The laws that discuss inheritance are very, very, very specific in Islam. Many verses in the Quran and Hadith discuss this topic. It is a set practice that has to deal with fractions, kinship, and faith. There are a library of books on this subject, in Arabic and all languages. One that is well written in English is The laws of Inheritance in Islam by Sohail S. Hussaini.
If we summarize the rules of inheritance in its simplest form, only Muslims can inherit Muslims. A Muslim cannot inherit a non-Muslim and vice versa. One is not free to do as one desires with what one leaves behind. Whether you liked or disliked a next of kin more than another does not count in dividing the inheritance. Yet, one is allowed to dispose of one-third of one’s wealth (without leaving it to an inheritor). One can give it to charity, to a person that is dear, to be used as funds for orphans; as long as it does not go against the will of Allah.
However, it is not these aspects that upset critics (often, these aspects are never even mentioned), it is the fact that a woman inherits half of what the man inherits.
They request from you a [legal] ruling. Say, ” Allah gives you a ruling concerning one having neither descendants nor ascendants [as heirs].” If a man dies, leaving no child but [only] a sister, she will have half of what he left. And he inherits from her if she [dies and] has no child. But if there are two sisters [or more], they will have two-thirds of what he left. If there are both brothers and sisters, the male will have the share of two females. Allah makes clear to you [His law], lest you go astray. And Allah is Knowing of all things.
Surah Al-Nisa (4 – 176)
This is fact, but in context. The man inherits twice as much as the woman if both are of the same level; meaning, brother and sister, father and mother… However, the children (including daughters) of a deceased person would inherit, while the deceased person’s brother would not. A deceased person with no parents would leave an inheritance for his sister and daughter, but not for his cousins. Therefore, there are multiple contexts where a woman would inherit more than a man. But if they are of the same level; the man inherits twice the share of the woman.
Let’s look at things in an Islamic context. The responsibility and burden of providing for one’s family are put on the shoulders of the man. Therefore, his monetary obligations are already superior to the ones of the woman. Secondly, a man is not free to spend his money lawfully as he wishes (due to his obligations); while the woman is. A man that has a sister that is not yet married, or parents that are not able to sustain for themselves, is obligated to aid them; while the woman is not. A man is obligated to use his inheritance to meet the immediate needs of his family; while the woman is not. If the inheritance is money, land, or property; the woman has her claim to all just like the man. However, I don’t see anyone (Muslim or not) gathering to protest these obligations and restraints put on Muslim men… Why? The long and short of it, just as the end of the Ayat goes:
“And Allah is Knowing of all things”