Crossfit is adequate if your goal is to be "in shape." I say adequate because there are better, and cheaper, ways to do the same thing.
I have two issues with Crossfit though. One of them is the same issue I have with cardio for getting in shape. The other is related, and that's that it's not focused enough. Really these are the same issue, but I couldn't figure out a way to explain it otherwise.
So, why do I dislike cardio? There's no progressive resistance. You have your body weight and that's about it. You can increase your distance or the incline, but that's as far as you can go. Your body will quickly adapt to those and then you're done. At that point, it's basically just burning calories and wearing out your joints. Crossfit does have added resistance, but that brings me to the second point, which is that it's not focused enough.
The Crossfit WOD's are all over the damn place. Take a squat for example. Crossfit absolutely includes weighted squats, and that's great. The problem is that you may squat once every 2-3 weeks. That's not nearly enough to actually make any progress in it. Crossfitters will make SOME progress, but it's severely limited by the frequencies that they actually do things. Back to my first point, Crossfit suffers because it's more concerned with reps than it is progression. By that, I mean instead of setting goals for a workout of lifting a higher weight, it's almost always a goal of doing more, faster. For a beginner, you should be having linear progression. Time shouldn't make a difference.
That leads into the issue thateveryonehas with Crossfit in that it's dangerous. If your goal is just to do as many deadlifts as possible in a 5 minute period, your form will breakdown and you'll get hurt. Dumb.