You certainly have the right to contest the will. However, your own description of your relationship with your father as "estranged" will probably make such a challenge difficult. Generally in this instance a will can be challenged on two grounds: that the person making the will lacked the mental capacity to do so, or that the person was subject to "undue influence" by the person who benefitted from the will (or someone married to or a domestic partner of the person who benefitted). There also deadlines and procedures that must be complied with; failure to adhere to these deadlines and procedures will result in the forefeiture of your rights. See www.lawfang.com and check out my blog (which has posts on various issues relating to will contests and undue influence). Please also read my article on avvo.con on challenging a will in Massachusetts.