Generally, the surviving spouse inherits from the decedent spouse free from Estate Taxes.

Assets passing because of death receive a new stepped up basis for capital gains purposes. Furthermore, for all community property the surviving spouse's half interest also receives a new stepped up basis. In other words, for community property the entire asset is given a new stepped up basis for capital gains treatment. If it is then liquidated, there would be no capital gains income and therefore no Income Tax due.
A surviving spouse will inherit all estate assets tax free. An individual estate below the exemption amount shall pass to any heir tax free. With proper estate planning a couple would be able to shelter twice the exemption amount, set up a gift giving strategy while they are living, and take full advantage of a projected new basis on all community property to shelter their estate from Estate Taxes and possibly, future Income Taxes as well.
Shelter your estate from taxes wherever possible. With proper planning you may be able to shelter your entire estate from Estate Taxes or, at least, take full advantage of the Life Time Estate Tax Exemption, the Annual Gift Exclusions and all other possible deductions and considerations.