A lot of bands that are perceived as Satanic are usually anything but. Black Sabbath's Tony Iommi has his interest in the subject, but is not a satanist, Marilyn Manson is a priest of the Satanic church, but I don't buy his commitment beyond its use as a marketing tool, Glenn Danzig has been said to be a Satanist, but I don't really buy it from him either. Then there is Behemoth, which strike me as more anti-Christian than Satanic. What does this have to do with Ghost? Well, they could possibly be the real deal. From their lyrical content, artwork, costumes, and the fact they are not named all seems to point towards something a bit more legitimate. It is also possibly they are just really good at making the perception appear to be reality.
In the end, I don't think it really matters all that much. At least not to me. The bottom line is whether or not the music is any good. In the case of Ghost's debut album, Opus Eponymous, the answer is very good. It is strongly reminiscent of the 1970's, kind of like a mixture of Black Sabbath, Pink Floyd, Blue Oyster Cult, and Mercyful Fate. It is crisp, clear, fuzzy, and very groovy. Layer in themes of Satan, sacrifice, rituals, death, and witches and you have the makings of an interesting brew.
They eschew conventions of modern metal. It is like they have ignored a few decades of rock and metal progression favor of a late 70's identifying sound as their vehicle of destruction. It is not fast or extreme, not exactly technical, and not low-fi. This is a band that has come together with a singular goal and they go after it with absolute sincerity and eloquence. They do not sink into cliches or the usual retro-rock/satanic schtick that other acts have used.