YoWA has various themes to choose from, and you can personalize all your conversations, giving each one a unique background. On top of that, you'll have access to loads of emoticons, be able to send full size full size images and videos, and send multiple images at once (sending up to 700 simultaneously). This app also allows you to hide contact names and increase the font size.
Other than all the esthetic improvements and new features, YoWA works almost exactly the same as a normal version of WhatsApp. In other words, you can call any of your contacts, send text messages, voice messages, images, videos, etc. You could easily swap the basic WhatsApp client for this improved version and start texting your friends almost immediately.