I have been searching for a decent range of workout DVDs since 1994, and in most of that time, have only come across a precious few that I could repeatedly use that both challenged me enough to meet my appetite for a burn, and that I did not get bored with after so many times. Over the past few years I have discovered interval training as the way to go: more intense workouts combining strength and cardio = less time working out and faster, lasting results. Or so it seems for me. I've run through this DVD fairly consistently for over 4 years, and find it challenging enough to get a solid workout, and while I got tired of the music pretty quickly (as is the case with any workout DVD), from start to finish I find that I'm not bored but actually looking forward to each final completion because I know it's a solid range of interval levels to accomplish.UPDATE: About 1 year ago I discovered Michelle's Peak 10 workouts and have essentially replaced this DVD for that in order to increase my level of challenge and pain, mostly because it seems more hard core and broken into more manageable chunks for when I may only have 20 minutes to get an intense work out in before headed to work or before calling it a night. I still use this (Best Body Circuit) for the days when I have an hour or more to put in the whole time or to mix up the routines. All in all, have been very pleased with the videos from Michelle Dozois!