After reading his review, it's hard to tell.
Mossberg reviewed the HTC First, the first smartphone to launch with Facebook's Android take-over software pre-loaded. For the most part he skipped talking about the hardware, which is just middling. He focused on the software.
On the one hand, Mossberg says, "I found Facebook Home to be easy to use, elegantly designed and addictive."
On the other hand, "I found some downsides," says Mossberg. For instance, you can't get quick access to the camera. You can't put weather widgets on your lock screen, and you lose access to a grid of commonly used apps in your home screen.
The negatives seem to outweigh the positives, here.
But, Mossberg concludes by saying, "Facebook Home is a very clever and very well-done product that will delight Facebook fans. If you aren’t in that category, or prefer the standard Android user interface, it won’t be right for you."
So, basically, if you're a hardcore Facebook user, go for it. Otherwise, skip it.
P.S. We'll be getting our own review unit shortly, so we'll have a full review of our own.