Personally I think Islam is an Abrahamic religion in that it partakes of the same stream of monotheism as surviving Judaism and, to a lesser extent, Christianity does. Frankly it borders on idiocy or perversely insulting bigotry to suggest otherwise, given the clear shared cultural milieu of Near eastern religious currents present across the "big three".
Even more personally I believe Abraham, or his inspiration, was an enthusiastic son slaughtering incestuous polygamous polytheist. I believe that part of the story was remodelled for the benefit of the later monotheists who adopted and monopolised their/xyr legacy.