The text under the toolbar buttons can be hiddent by unchecking Show Toolbar Text Labels. The thumbnails on the measurement tabs can be turned off by unchecking Show Thumbnail, in which case the tabs only show the measurement number. When thumbnails are shown a grid can be overlaid, which can help gauge the span of the data, and shadows can be drawn under the trace name text by checking the relevant boxes. Animate Task Panes controls whether the task panes (Trace Adjustment, Target Settings etc) slide open and closed.
The Look & Feel setting changes the appearance of REW, which by default takes on the Look & Feel of the platform it is running on. The change is applied immediately, but there may be some details of the layout which do not fully update until REW is next started.