I did a P90x for about half the program, though this was before I found Eat More to Weigh Less. I had never really lifted before that and I found that I was definitely getting stronger. There's not very much cardio at all, just two work outs out of the six, and they have more "bursts of intensity" than consistent cardio.

So, if you don't have access to a gym, I'd call it good enough! I went from being able to do only 5 push ups on my toes to 12, finally managed a couple chin ups, and the yoga actually really increased my flexibility. You will definitely build some muscle in this program, especially if you listen to Tony and "pick the proper weight to get the job done".
That and, of course, fuel your body so it can build that muscle!

My guess is that straight up weight training at a gym would build muscle faster, but I have no basis for that other than thinking squats/deadlifts etc...with a lot of weight are just better at building muscle than using hand weights/bands like in 90x. However, p90x has the added benefit of a program to follow and workouts that increase flexibility and overall fitness (like pylo and yoga).

Hope that helps! I enjoyed doing it and still do some of the workouts at home. You might just want to mute Tony after awhile.

P90x is a great program to get into a routine since it pushed you to follow the program. I am currently on my second round of it (p90x/insanity hybrid actually) and really enjoy it and its a nice break from the gym. The cardio is a bit off if you have done Insanity or some other crazy program thats all cardio but its hard if your just starting out and will still burn enough calories to make you feel it. Like all home workout programs, you get what you put into it.. so you really need to work.

As for the isolation work emphasis, they do have individual days for body groups.. compound work is great for working the whole body, but the thing that isn't mentioned much is compound work doesn't normally push your maxes of those groups as an isolation workout will do.. they both are beneficial, that is why some people will do compound movements 2 days, then isolation 2 days kinda thing, or week by week.