I've been using Google Slides quite a bit lately and I'll be on to Office365 next, but here are some power user tips:
- The themes are really powerful, but you can many themes with the same name. There is an invisible GUID for themes, so when you are confused about formatting turn on the themes and then click on the "In this Presentation" button, you will probably see many themes of the same name. If you delete all but one, then things will be sane again.
- Deleting lists. Lists in this product are really strange. You can add them with the GUI, but there appears to be no way to get rid of lists. In a slide, you can use a keyboard shortcut, CMD-SHIFT-7 but this does not work in a theme. Very strange.
- Images are really easy. You just go and give it any link, but the tricky thing is you can actually crop images to shapes. Just click on the crop icon on the right and you will see you can crop to any shape. It is not in the format images menu though so hard to find.