The Hyundai NAV screen is 6½". I've had cars with 7" and 8" screens in the past so it's a little small. But it's not TOO small. Compared to the hand held units it's enormous.
Overall I'm pleased with the system. The most important thing to me is the fact that it's not locked down while driving like many of the other manufacturers. Anything you can do when standing still you can do while moving. This was not the case with the Toyota or Nissan units I had. My Acura was close, but there still some things that got disabled while moving. The Hyundai is fully unlocked.
The voice recognition however leaves something to be desired compared to the Acura. But it's far and wide superior to the Toyota. The really nice feature of the Acura was that any button you saw on the screen could be addressed using the voice except for actual letters. You can do most things via voice, but it's not as intuitive as just seeing the screen and pushing a button by saying the button name.
But the NAV offers more than just navigation. It offers a far superior display for the audio and bluetooth systems. I really use the NAV pretty seldom, but I love what it offers, particularly for the audio system. And if you are getting the Limited, the backup camera is shockingly useful. I thought it was going to be more of a WOW gadget, but I've really utilized it a lot. Just the other day I got stuck in a circular driveway and had to back out. It would have been a royal pain without the camera. It's great for backing out of my garage and for those time when I need to parallel park. It's just a wonderful addition.
Your own mileage may vary on how useful the XM traffic is for you. It only does major interstates. Even though XM has traffic data for many surface streets the Hyundai setup doesn't utilize it. Since my daily commute is all off-highway, I let my subscription lapse. Others might find it useful. The few times I did get a chance to use it though it was kind of nice.
Directions themselves seem to be pretty good. This is the 4th in-car NAV unit I've had. On all of them you'll find that if you're really familiar with the area you can route yourself better than the NAV unit. But if you really don't know where you're going, it will get you there. And that's really all that counts. I've had some that have had major errors such as telling you to exit an interstate and getting right back on for no reason at all. My Acura did this in one spot and it actually cost me an extra toll the first time it happened. I haven't run into this yet on the Hyundai.
The POI database is so-so. I've had a few things I tried to lookup that I thought should have been there but weren't. But all units have some holes. But when embarking on a journey, it's always good to be armed with the actual addresses rather than relying on looking it up unless you're sure it's there.
Overall, it's a pretty good unit.