A video showcasing all of the available soldier customization options (except female faces, for some reason). It talks about them as well, and has a small interview with Jake Solomon.
This game allows you to create a pool of characters who will be reused throughout multiple playthroughs.
These characters can be soldiers, scientists, engineers, or even enemies to capture or kill, depending on how you set them.
So even if you can't get the game just yet, you can choose how you want your character to look, write up a Biography for them, and choose their class (which you can also set), and I'll stick them in the game when I start streaming and recording it after launch.
The class options and ability selections are also provided in other videos that he did. Firaxis already mentioned all the classes, but I'll spoiler them, in case you want to go in blind (and to save space on the page).