Cons: GPS isn't free, it's pretty thick.
I'm loving the selection of messaging devices this season: Propel, Gravity, Slate, Quickfire, Rant, and Matrix are a few off the top of my head, but I know there are more out there. If you're heavy on text and into the novelty of experimental form factors, the Matrix should be at the top of your list.
The software works well, and offers a no-frills interface for getting things done quickly and simply. I see an odd 3D effect when I have the screen in landscape mode, but it's possible that I just need new glasses. I've been using this prescription for at least four years. The colors are bright, and the display is fine for a phone at this price.
For those who haven't seen the Matrix or Duo, this one is a dual-slider. Push the face up, and you get a standard, but very cool, telephone dialing pad. Close it and push the face to the right, and you're presented with a full, slightly-angled-grid-style QWERTY. The display goes into landscape mode when the keyboard is out, and there are two keys at the upper corners for contextual menus. Take a look at Noah's video for some beefy tunes and a better idea of how the Matrix is laid out.
I personally prefer phone keyboards with a staggered pattern, like those seen on most desktop and laptop computers. But this one feels nice. It's a tactile surface, and I was touch typing by the end of the first day. I like the materials Pantech used for the keyboard. The keys feel great, and the design of the body makes it really easy to access the QWERTY. It's very comfortable for typing long messages at high speeds. There's nothing in the way, and the compact keyboard doesn't give me cramps.
As for the cam, it's good for quick, on-the-go snaps you want to send off to another phone. I'm not a big fan of the Matrix as a music player, but it works. It is a messaging device, and the price is right. It's just the kind of phone I'd get as a gift for my wife to make texting easier on her. It's great for IM, email, and MMS as well, so it really is a complete messaging package. I wouldn't pay for the GPS, though.
The Matrix is a hefty .83" thick, but if you wear loose pants or carry your phone in a purse, it probably won't be an issue. It didn't bother me in my somewhat baggy jeans. It's very close in size to AT&T's Fuze, so if you've held one of those, you've got an approximation of the dimensions of the Matrix.
Verdict: two texting thumbs up.