Apparently they ruled out 21 other landing sites before selecting the "Elisium planitia". The selection process included being served up some plain old surface where the heat flow could be measured, seismicity wasnt loaded with local structure that would attenuate signals and the tectonic returns could be measured to evaluate their sources. Only a little of the deeper probe will be devoted to geochemistry and that will (I understand) be focused on silicates.
Apparently the last three sites to be let on the "final contestant" list had som engineering realities to contend with, sunlight array, and low winds.
So, as they said at JPL, "If Elisium Palnitia" would be a salad, it would be lettuce and kale, no dressing. But thats wxctly the kind of site we need to do deep investigations by seismic reflection and thermal gradient detection"
Most often, long term science data can be amazingly boring>(Im sure the newspaper science reporters will pimp it up for the average kid and parent)