Richard Gabriel's Jesus the Egyptian (JTE) proposes yet another thesis that Christianity borrowed all it owns from Egyptian religion; the only question therefore is not "Is it nutty?" but "What type of nuts does it take from the tree?"
We should begin with a preliminary comment on the author, who is a professional historian: But a specialist in military history, and thus writing well outside his expertise. We should also note that it is put out by iUniverse, despite Gabriel's past record of credible publishing; take that as a signal that he'd never have gotten it done with a serious academic press.
Finally, note that unlike every other version of the "copycat" thesis that connects Jesus and Osiris, Gabriel is not a Christ-myther; rather, he supposes that Jesus did exist, and while living in Egypt learned about their religion, then started his own countercult(ural) revolution against Judaism because he was offended by being treated badly by his neighbors and kin. More on that anon. Let's start with the basics.
JTE consists of 130 pages, 100 of which could have been shed and made the book much less tedious at once. Those 100 pages are too-detailed recountings of Egyptian history which do little or nothing to add to Gabriel's case. The remaining 30 pages are Gabriel's case for borrowing.
The case is more general than specific in this one. Gabriel thinks that Christianity borrowed six elements from Egyptian religion :
- a single trinitarian god
- a cosmology in which all things have a place that can be comprehended by man
- man's possession of an immortal soul
- resurrection of the dead
- a final judgment where ethical life is weighed
- eternal life for the virtuous
- Failure to recognize practical universal concepts (all except 4) -- Gabriel actually goes as far as saying that all other cultures of that time and place -- such as the Romans and Greeks - borrowed ideas like an immortal soul from Egypt , which places him in the range of lunacy espoused by the likes of Yosef ben-Jochanan. One is constrained to ask what Gabriel supposes people believed in this regard until the Egyptians allegedly enlightened them. And who informed the Aztecs of the notion? It's clearly one of those things that is arrived at independently as a matter of practical deduction.
- Redefining terms to a least common denominator to achieve a parallel (4-6, on 4 especially, see October 2009 issue, "Defining Resurrection")
- It envisions Jesus as a radical individualist in a time when collectivist thinking was all that was available.
- It must suppose that Jesus was put on trial for disputing Jewish "monotheism"  -- a questionable category to apply to Judaism of the time to begin with (here again, Gabriel is unaware of the thesis of hypostatic manifestations of deity in Judaism), and also found nowhere in the NT text among the accusations delivered by Jesus' accusers, or in the secular record of Josephus. If anything, it was not so much that Jesus claimed this identity per se; the problem was that he was claiming honor over and above his station by claiming that identity.
- It forgets to explain the step wherein Jesus preached belief in Osiris and Isis, and somehow made himself the object of faith, as opposed to Osiris or Isis.
- Gabriel makes the astonishing claim that Jesus is rarely depicted as practicing Judaism in the Gospels . What about his teachings in synagogues as an adult? What about his profession that he came to fulfill the Law? What about his disputes with the Pharisees over fine points of Jewish law, and absolute mastery of the OT? What about his direction to Peter to contribute to the Temple tax?
Finally for our sample, Gabriel supports his case with standard misreadings of passages like John 2:4 and Luke 14:26 to argue that Jesus hated his mother and family. 
In sum, while the ride Gabriel offers us is nowhere as wild as that offered by, say, Acharya S, the scholarship he offers is quite nearly as dismal.