There's so many positive things to say about this product it's hard to know where to begin. I'll try to avoid covering too much familiar ground of the other reviews. So let's start by saying this: It absolutely works. What's great about this program is that it addresses ALL your fitness needs. Whereas most workout videos/programs tend to focus on either strength training or cardio or flexibility or target specific areas, P90X does it all. Just be aware that you'll have to invest in a pull up bar (although alternatives are given for substituting power bands, but nothing beats the bar), some dumbells or power bands (the bands work fine if you're looking to tone up or travel with them, but for people really looking to do some work and get their Bruce Lee on, dumbells are a must), a yoga mat, possibly some push-up stands (they're worth it, or you can just use your dumbells if you have the kind shaped like a hex or a square), and a heart-rate monitor isn't bad either. I'm 30 and I've been an avid gym rat since I was 15. This thing beat me up the first time through. Plus, I'm flexible like I've never been before which makes life so much better getting out of bed not being stiff. Best of all, my abs are chiseled better than when I was 20. Tough to argue with that. Alright, enough about me, I think one of the strongest points of this program is it's level of customization.
The way the program works is this: For the first three weeks you'll do strength training workouts on days 1,3, and 5(each bodypart being worked once per week with the exception of the back-you're gonna do A LOT of pull-ups/chin-ups). On days 2,4, and 6 you'll do some form of cardio (yoga, plyo, kenpo). And then on day 7 you have an optional stretch. Then on week 4 you completely remove the resistance days and they're replaced with other types of cardio and stretching (the Core routine is amazing). In weeks 5-7 you keep the same days 2,4, and 6, but you have all new videos for the resistance days so your muscles are forced to adapt and grow and avoid plateauing. Week 8 is the same as week 4, allowing you to catch up for the final push. Weeks 9 and 11 are the same as 1-3, weeks 10 and 12 are the same as 5-7, and then there's the final week, same as 4 and 8. I know it may sound a bit confusing, but it's all laid out very clearly and concisely in the accompanying book. Plus, you'll be doing abs on the resistance days.
What I just described is called P90X Classic. It's the standard arrangement of exercises. Again, here's where the customization comes in. If your goals are more weight loss and slimming down, the book rearranges the videos into what's called P90X Lean, de-emphasizing the resistance training in favor of the fat burning. And for those truly "touched in the head", there's P90X doubles. This has you doing 2 programs per day on certain days, one in the morning and one in the evening. This is truly the ultimate challenge (but also a bit time consuming as you'll need more than 2 free hours per day to dedicate to exercising).
Another great feature of the program is the inclusion of Cardio X. PlyoX is, by far, the toughest of the cardio programs. It will chew you up and spit you out the first few times you try it. For those that find it too difficult or may have some joint issues preventing them from jumping, Cardio X is designed to be a low-impact substitute. Throughout all the different programs, Tony and the crew will show alternate exercises for people that may have some health issues (knees, shoulders, etc. . .).
Some people wonder what's next once they finish. Good question. For most, you'll benefit from going through the program one more time as is. Or, you can try the lean or doubles. Maybe just do the classic again, but try and do things double-time or increase your weights a good deal. It'll probably be a month or so before you're able to truly begin to keep up with the videos the first time through-and then they switch it up on you (that's the beauty of it). So doing it a second time allows you to go hard from day 1. Also, Beachbody is releasing P90X+ in Dec. 07. These are 5 new workouts that you can substitute in to the existing infrastructure. But, be aware, these are for people that have already gone through the entire 'X' or are in world-class shape, as they are more difficult than even their predecessors were. They were designed specifically with the intent of building upon the foundation laid by P90X, by no means are they a jumping on point. Plus, they don't replace all the existing videos, so you would be far from a complete set should you choose to grab just the + programs. But hop over to youtube and put in P90X+ for a preview (I get tired just watching). With the inclusion of these videos, the ability to mix and match as you choose to in order to meet your goals, and the format that allows you to determine intensity and speed, you'll be able to keep your workouts fresh for a very long time.
And once you've gone through the program, you'll get an excellent feel for what each video does and how to customize the program. You may want to increase your flexibility by using the Stretch X and Yoga X a few times per week, supplementing it with some cardio and strength work. Bottom line, the choices are yours. Just remember, these are not for beginners and you will need an hour per day (hour and a half for yoga)-no "30 minutes 3X per week" nonsense here. If you head on over to the P90X website (just google it since we can't use URL's), click on the picture about half way down that says "Learn more about P90X" and then click on "Is P90X for me", there'll be a link to a PDF of the fitness test you can do at home that will give you a good idea of whether or not you're ready to begin the program.
Even with the additional equipment to buy, it is well worth the money. Remember, you're not expected to be able to keep up right away. It'll be quite a while before you do. Go slow and at your own pace. You are encouraged to just keep with it, even if you can only do 1 pull-up, do it and wait for the next exercise to begin. Just stay with it and you'll be amazed at the progress you make. The last thing you want to do it burn yourself out right away. When I first got the program I spent 2 weeks just "walking" through all the routines (and I was still spent). One final note, just be careful if you live in the upstairs of a building as I do, it can make Plyo day a bit disconcerting for the neighbors beneath you if they're not expecting it ;)
One last note because I've seen some of the negative comments on here: Buy it from the official site. Just say no to all the special offers so you don't get billed for anything extra (I declined all offers and have never had a single problem with extra charges). Just buy it from the regular site at P90Xdotcom.
Update Mar. 2010: There is no doubt as to the longevity of P90X. I've gone through round after round and it is still difficult. It feels like the harder I push myself the harder it pushes back. I had some friends pick up the Tony Horton One-on-One series and the Insanity series (both from Beachbody). I tried doing just Insanity for a while but I couldn't live without the resistance exercises. While the cardio pushed me hard, not having weights just didn't work. So what we've done is take the One-on-One's and the Insanity and work them into the P90X structure. 3 resistance days with abs (each body part at least once per week), 2 cardio days, 1 yoga day, 1 optional stretch. And that's it. I can still get cramps and be sore the next day if I push myself, especially in plyo. It never gets easy, I promise. So just "keep pressing play".