Kabalah or at least Kabalistic ideas are actually the majority opinion in Jewish theology, as distinct from Maimonideism (which is basically Jewish Scholasticism). It can be Orthodox–Hasidic Jews are Kabalists–but it’s not particularly *good *theology.
Were it Protestant, we’d have to call it fundamentalist. And not a very nuanced fundamentalism (most fundamentalists actually have a very subtle if informal understanding of scripture). Kabalah as found in the Zohar teaches that all statements about God in the Bible have literal truth: he really is named I AM, for instance, as well as Peace, Truth, and all the other titles. Maimonides understood that that’s impossible; humans cannot fully understand God because God is a pure, unalloyed concept and the human mind, being itself composite, can’t conceive of anything noncomposite.
Kabalah also teaches that God’s being has ten layers or “Sefirotim”, which are basically just aspects of Him or tasks he does. Of those, some Kabalists say that three are bad, three are good, and four are neutral, while the more Orthodox, thinking it blasphemy to ascribe any evil to God, merely say that three are dark and three are light. At the end of the day, though, all they’ve really come up with is the yin-yang-mu distinction of Taoist philosophy.
Fullblown Kabalah (as opposed to a Kabalist strain in more mainstream theology) probably didn’t become the majority view until the sixteenth or seventeenth century, when a famine and depression hit Poland (where most Ashkenazi Jews lived–also the only European country that let Jews become nobles) and the rest of Eastern Europe.
As is typical in times of despair, the Jews, and the Gentiles, too, turned to mysticism, not to say superstition; it was at that time, also, that the big Vampire scares happened throughout the Austrian Empire. In neighboring Bohemia, Rabbi Lowe of Prague was said to have made his famous Golem, using his Kabalistic knowledge of the Divine Name (I think he was a Ba’al Shem Tov). And in northeast Germany an alchemist by the name of Konrad Dippel, who had been born in a castle called Frankenstein, got chased out of his university for robbing graves and attempting to animate the dead. I’m not kidding.
That’d be why Kabalah’s so, well, odd, but it can be practiced (very carefully) by fully orthodox Jews. Its potential for misuse, as by Madonna, is the reason it was traditionally esoteric, forbidden to all but elderly, extremely learned and righteous rabbis.