A couple of videos recently posted by IGN shows two gameplay elements in Mass Effect 3.
The first is the galaxy exploration part of Mass Effect 3. The interface and look is still pretty similar to Mass Effect 2 but you won’t be mining for minerals rather you will have a new scanning device that allows you to detect hidden assets in a system.
You can launch probes to acquire war assets, artifacts, intel and fuel. War assets will have an impact on the ending as it contributes to your galactic readiness rating. Using the scanning tool will also alert reapers to your location.
The second video shows some combat gameplay from a mission on the planet Mars.