First, the Roth IRA does indeed "pass through the estate," in that it is considered an asset of the estate for calculating any estate taxes that may be due. I think what you mean to say is that the IRA does not go through probate, since it passes to the named beneficiary by contract rather than through the decedents will.
If the Roth IRA has been in existence at least 5 years, as the beneficiary you can take tax-free withdrawals, even if you are under 59-1/2 years of age. If the Roth IRA is less than 5 years old you only have to pay income taxes on the portion of a withdrawal that is attributable to earnings.
If you are the spouse of the deceased, you have the option of rolling the inherited IRA into your own IRA (in which case you can't start withdrawals without penalty until age 59-1/2). If you are not the spouse, you are not allowed to roll it into your IRA, but must keep it separate, and you are required to meet certain minimum distribution requirements, such as either taking a complete distribution within 5 years of the previous owner's date of death or setting up a series of payments throughout your lifetime.
Here'a pretty good web site that provides details:
Inherited Roth IRA