I've just started using Publisher (long-time Pagemaker and InDesign user).
One feature I can't seem to find which is pretty critical for some of my work is the ability to crop the frame of a linked image without resizing the image.
I.E. I have an image that would take up a full page, but I only want half of the image to be shown. In InDesign, I could just grab the side of the frame and drag it to the size required without altering the appearance of the remaining image (or I could tell it to fit the frame afterwards if I wanted it resized). Often, I can't just overlay it with a box coloured to the "paper" colour as there would be elements behind that would need to be seen, and I'd rather not have to make a copy of the image with the appropriate reshaping.
Also, Transform needs a % change option.
Otherwise, my first impressions of this program are pretty good :)