For one that has already used Windows Phone 8.1 will have a shock when they start to type and the comma is nowhere to be found. Instead, you either need to type "&123" or press long on ".". This is too troublesome to type even normal sentence.
Apparently, this can be changed easily. Just go to settings > keyboard > advanced, and check "Show a comma key when available".
I think it's better to display comma as default, and give option for user that needs bigger "space". If I don't really search into this, I will not know this can be displayed back and only can curse somebody at Microsoft for hiding the comma.
One changes that I like in addition to "swype" feature is the cursor key. Previously, you need to press and hold for few seconds then the flying cursor appear. Now, there is one small circle below the cursor, just press the circle and drag. Nice..