The obvious direction for a robot game is something like Transformers. Reasons:
1. Already a fan population
2. Already movies to appeal to the imagination

Now, if the trademark is too expensive (likely) you can still make robots that "switch modes" into a much more mobile yet non-combat version. So turrets fold in and four wheels sprout out. Then your robot can move/fly at three-four times their base speed at the expense of not being able to fight. This also has the benefit of making the game more fun because frankly, the slow travelling back and forth to waypoints for missions is such an obvious timesink that it's insulting.

As for the Global F'ing Purpose Of It All...well obviously robots would of opposing ideals need rare metals to repair/maintain/build themselves. Competing over resources is therefore the obvious goal. Say that these robots finally found a world rich in these rare elements (and you might as well use real elements like titanium, gold, etc). So then you form a corp > gain sovereignty over a region through kicking tons of *** in pve missions there > the security rating then slowly rises to 1.0 and some friendly npcs spawn (Concord) and attack opposing factions that enter, but they are only strong enough to handle small groups of 1-3 not a full gang invasion > The security rating also slowly degrades but this can be countered by continuing to do 2 pve missions/member per day > Then once sec 1.0 you can start to build permanent defensive/industry structures which are destroyed if the security rating falls below .5

That would be more interesting to me. Random pvp and pve growth has been done to death.