Microsoft says the preview is built off “the core of Microsoft Lists,” and comes with some new features, including tabbed views and the ability to add images in-line. The preview isn’t a feature-complete version of Lists, unfortunately, as Microsoft mentions that it’s missing some functionalities of the standard app (although it’s not clear exactly what). It’s also not available on the iOS or Android app yet.
If you do decide to try out the preview, keep in mind that there are some limitations on storage — rather generous ones, at least. You can create up to 50 lists with a limit of up to 2,000 items per list and can upload up to 200MB worth of videos, files, and images to each list.