I find that a lot of IRs tend to lack low end resonance, or if they have it, it sounds a bit cheap, and has no real weight to it, almost like it was a post-eq rather than the character of the cab/mic combination. The high end is even trickier, you either get very dull captures, or ones with so much unusable "air" and high frequencies with all sorts of whistling frequencies which you then have to notch out (but notching can really neuter a guitar tone...) The ML IRs just nailed both of those making very usable IRs right out of the box, and mixing them was so much easier because I wasn't dealing with weird and unpredictable characteristics. From personal experience, I can tell you the room an IR is shot in makes ALL the difference as well. For example, I have shot my zilla cab in my studio (before it was treated) and then I shot it in a professional live room, both with a 57 in the exact same position, and the one shot in my untreated room is ugly, bright and notchy by comparison. The room being used in the ML IRs is a damn good sounding one too!
