Actually, as someone who considers himself a Christian theist, I thoroughly enjoy[ed] this series. 'Suspension of belief' is required, but this is the way for most books/movies regardless.
Do I find this manga offensive?
Not in the slightest.
Perhaps quite the contrary, this is a very enjoyable, and rather lightweight .. story [used loosely] about Jesus and Buddha sharing a apartment. Other than the obvious religious themed jokes [i.e Buddha winning a giant statue of Buddah at Disneyland, Jesus being afraid to swim (hence walking on water)], it manages to develop a interesting relationship between the two.
It's religious deity buddy comedy manga at it's finest.