On Marine forces:
I am a bit torn, honestly. While I definitely see the efficiency of starship defence and attack and not necessarily needing ground forces, I do lean towards to the precision of marine-type forces as well. I think one of the "problems" with making a Trek MMO universe of the sheer grandness of it and having to focus on both ground and space in great detail and then integrating them together. At this time I too think that ground wars in the Trek universe, especially in our supposedly future timeline, won't be the bread and butter of war.
More on FPS vs RPG:
In my opinion FPS and RPG just don't go together very well, especially in a MMO setting. I.E. The current Star Wars Galaxies gameplay. To me it is very give and take and they are seperate genres for a reason: they are two very different gameplay styles. When SWG tried it the combat felt very shallow and you lost most (if not all) of the depth, I don't want to see the same happen to STO.
On the other hand, I think a suggestion was given to switch to FPS for certain missions (possible implementation for holodeck pick-up duels?) etc. I think since you would be completely changing to that style of combat and not trying to merge the two together that it would work in that instance. But with everyday play, I just don't think you can successfully compile RPG and FPS into one style of gameplay, you need to choose one or the other to have it feel solid. However, I would love to be proved wrong and am eager to see how they deal with it in STO.