White balance, countdown timer, time-lapse mode and Scene settings have been removed in this app.
Also the reason for the large shutter button is that earlier the image was cropped inside the viewfinder. But now they are trying to show the full 4:3 preview inside a 16:9 display which means they can't expand it to take full screen without cropping it up like in the Nexus 5 (as sushubh mentioned). So even if the shutter button is bigger, the image you see is the full proper image you are going to click.
Source
Also the reason for the large shutter button is that earlier the image was cropped inside the viewfinder. But now they are trying to show the full 4:3 preview inside a 16:9 display which means they can't expand it to take full screen without cropping it up like in the Nexus 5 (as sushubh mentioned). So even if the shutter button is bigger, the image you see is the full proper image you are going to click.
Source