I really like Insanity; however I find it very different from any other type of cardio I've ever done. It's hard to explain exactly whether it's harder. It seems to be, but I find it so hard I can't make it through most of the workouts without having to take my own 5-10 second breaks--which become more frequent near the end of the workouts. I never have to do that with any of Cathe's workouts, including Tabatacise. However, in many ways I find Tabatacise and her other HIIT focused workouts just as hard, becasuse I am going, going, going and never stopping for a break unless Cathe gives me one. I cannot do that with Insanity. So near the end I often feel I am breaking more than I want to be--but I am so wiped out!
So, in a sense, I feel they are equally as intense, but very different. Other workouts I put at a similar level are Amy Dixon's HIIT/tabata workouts and Michelle Dozois Peak 10 workouts. With these workouts I don't have to take personal breaks either, like I do in Insanity, but they are very difficult in the same way that Cathe's are (just not as fun as Cathe's!)
I will say that of all of the ones I've listed, Cathe's are my favorite. Her workouts just have more of a fun factor than any of other trainer. And I will agree with StaceyV, when I did the Insanity program, there was a big dread factor to the workouts. I also felt more recovery was needed between such high impact workouts. But when I use the workouts on my own--inserting them once a week as one of my cardio workouts--I enjoy them much more.