Are you using a VGA device? You'll need to download and install a VGA theme here.
If you are using a device with a 240px square screen, you'll need the a theme that support this screen size. What's different from other contact application:

• It can be used with fingers, no need to get your stylus. Finding contact with your finger is really easy, it's different than other software: if you press you finger on the left or right border of the screen it will allow you to select the letter you're searching for, release the finger, it will show you the contact starting with this letter. Why does it work? Human being cannot point directly to the right letter on a small screen, however human are very precise while moving their finger. So you press the screen, see the feedback, adjust the position to the right letter... and you're done!
• It's animated: the list scroll with your finger in a natural movement, the transition between contact detail and contact list are animated.
• You can set contact as favorites, they will appear in the favorite list, perfect to get a quicklist of contacts under the finger.
• You can edit your contact picture from the software, simply tap on the contact picture.
• You can customize about everything by changing the setting.ini: color, font, background image, etc...

From ContactManager here's what's new/modified:
- Native version: this version doesn't use .NET compact framework, it's written in C++.
- Faster version: I've put some time improving performance, on my device, it goes quite well, tell me about you.
- Faster display: drawing is also optimized, however, it may have some issue for advanced theming, tell me about it.
- New fade effect while calling/edit conact/set picture, this offer a better transition between application, tell me what you think.
- Contact update if added/changed/deleted from other application (including activesync).
- Memory footprint: No more .NET crap, picture of contact should also take less memory.
- Ability to remove contact picture.
- Edit contact now goes to edit page directly.
- New contact now goes to edit page directly.
- New theme packaging (a theme in one file instead of many).
- Letter bar between contact.
- New setting for non latin alphabet (coming with localization but now it's technically possible).
- SMS conversation panel: hitting SMS button now goes to an SMS page. It will allow to send an SMS display previous conversation with this contact...