The Daylight interface upgrade is primarily a visual change; some of the borders and buttons will have a new look and feel and a few will have new names, but the content of the courses won’t be affected. One name change you may want to note is that Dropbox will be renamed Submissions. All the tools and features will still be available, and some minor new features may be available.
The D2L site itself will now use responsive design, meaning it can scale to fit multiple device sizes (primarily affecting phones and tablets). Some content may not yet be mobile responsive, but when accessed from a computer, everything will appear much the same as it does now with only small aesthetic differences.
If you’d like to see a preview of the test system with some of your past courses in it, let me know and I can provide a link and instructions to access the test system. D2L also provided an overview video at https://www.d2l.com/resources/videos/the-brightspace-daylight-user-experience/ that shows some of the new interface on a generic system (ours will be a customized version of what you see on this page).