The Sentinel-3 constellation of Earth Observation satellites is designed to provide accurate and timely information to better manage the marine environment, and to understand and mitigate the effects of climate change by utilizing systematic measurements and products of sea-surface topography, sea-state and ecosystem characteristics over the open ocean and the regional and shelf seas. The aim of the paper is twofold: (a) to provide a brief overview of the types of data available to users from the current Sentinel-3 satellites, and (b) to outline the new features, compared to the conventional radar altimeters, and the new capabilities provided by the Sentinel-3 SRAL (SAR mode) altimeters. The presentation will show representative results based on comparative analyses using previous (conventional) and current Sentinel-3 altimetry data, in an effort to identify critical data handling aspects (i.e. data access) and associated constraints (such as primary outputs, ground coverage, etc.) vis-à-vis typical user requirements for various marine applications, especially closer to the coastal areas where the SAR altimetry method is shown to be superior to conventional systems in terms of accuracy, spatial resolution of the observations etc.