AutoCAD 2015 actually introduced what they call Ribbon Galleries, which are graphical drop-downs showing previews for items such as blocks, dimstyles, mleaderstyles, tablestyles, etc.
Although it sounds like a good idea in theory, in practice these gallery views proved to be slower and more cumbersome for many users than simply picking the desired object from a plain old list. Unfortunately, in AutoCAD 2015 there was no way to disable this feature.
Evidently there was a enough negative feedback and the AutoCAD team introduced a way to disable this feature in AutoCAD 2016. Simply set the new system variable GALLERYVIEW to zero. Kudos to Autodesk for listening and responding to their users, but they could have avoided all this by including this sysvar in 2015 when the feature was first introduced. Please don’t force UI/UX changes on us, let us decide what is more productive to us.