I haven't read Judas Grail completely, but what I've seen makes it well-nigh unplayable, so it needs heavy modification to be run. Or it can be used as a source for ideas rather than a whole adventure.
I don't think that KULT lends itself to out-of-the-box adventures easily. KULT is a very personal game (personal in relation to the player characters), and the typical CoC investigator scheme doesn't work well with it IMO.
That said, the problem with JG is (in parts) similar to that of early CoC adventures which were too laden with mythos critters to be playable. The adventure contains far too much opposition, it seems to be written by someone who wanted to include everything he finds cool about the KULT background. And then some.