Hmm, interesting. The basic plot doesn't seem to put Christianity in a bad light or anything (although I only read the first post), but that would still receive a lot of backlash. I myself am a Christian, but I'm intrigued by the story. However, I'd probably feel a little blasphemous reading it. But hey, maybe I'd read it anyway.
"IMO it is not, but I am worried about reviewer backlash..." If you are worried about reviewer backlash, stop writing. You are setting yourself up for heartache. You will get bad reviews. We all do. If this is your mindset, a bad review is going to do unnecessary harm to your psyche. Write for you and you only.
Christians who are of the older years and/or belonging to factions such as pentecostal and fundamental baptists will be highly offended, but keep in mind that the majority of Christians aren't up in arm and physically attacking atheist authors who claim Jesus never even existed, so you should be ok overall. However I think that since it sounds like your keeping Jesus as a good guy/savior of mankind type many Christians will read it just out of curiosity, especially the younger ones who are more open minded. And if you'd rather your book be in the "Fiction" or "Sci/Fi Fantasy" sections of Barnes & Noble rather than just the Christianity section, throw in some other figures too. Maybe Buddha, Moses, Mohammed, Krishna, were all people in a line of reality warpers trying to go back in time and unite man through religion to prevent the ultimate evil from taking over, maybe they're actually all the same guy who has to keep going back to various points in time because each time he's gone back has been a failure
Not at all, and I think it's an intriguing premise. There might be people who balk on instinct to such a thing (either they see it as too sacred, or as proselytising) but I suspect overall they'd be the minority. I don't sense a deliberate intent to offend at all - and that is something that would bother me - nor does it seem like some silly 'superhero Jesus' or something. I'm envious of anyone who can summarise as well as you have - very 'high concept'.
I think people would be very interested in it. Especially those that are faithful. There is a story adapted into a movie, i forget the name of it where this guy is immortal and he's trying to explain it to his colleagues. In the story it comes out he was Jesus in another life, but he never meant to create such religious turmoil. It was an interesting concept.