I have a custom folder content type that has a bunch of properties. If you are looking at the library you can select one of the folders and click on "View Properties" in the ribbon and it shows the normal display form and it's all great. But once you go into the folder, there doesn't seem to be anyway to get that same form? Do I need to make some kind of custom Ribbon command to do this, or is there some way that I am missing (other than go back up a level obviously)?
Out of the box it is not provided, once you are inside the folder you select items/folders/documents inside that folder and you can view properties for the selected.
You can of course create a custom Ribbon action to show the current folder properties, you can actually create exactly the same display as that of Display Form.
Like Arsalan said, there is no out of the box support for that. You might consider if Document Sets don't fit your scenario, since they have the Welcome Page that lists the selected columns at the top of the page.