This is a good foundation, but I think it would play even better if you could drive all the way around each main base. Are the rocks that block that path on each side really necessary? The interior of the main bases look like they could use some object use reduction, while increasing the aesthetic with new ones. Do you have a favorite UNSC base in the series? You could mimic its skin-deep design elements, while finding more useful structure to add. The man-cannon is okay, but it might do better in a different location. Maybe higher up?

I think you could put more obvious mid to low power weaponry around the map too. Also the canyon water kills vehicles. You might want to put an invisible blocker in it or raise the natural floor to reduce its lethality.

 

It's better now, good job. Some areas still stick out as needing an overhaul though. The sniper platform is thin and strangely doesn't touch the rock wall. You should also reinforce it with stuff. Similarly the man-cannon platform is raised, but it needs to be supported too. Maybe use a taller platform? The colored trim on the outside of the base is decent, but you should apply it to all of the main exterior corners and smooth out some of the hard 90˚ angles at the corners. The extra details like vents on the side should also be applied in a similar way to the back. I now noticed that some of the rocky terrain in the middle of the map could be difficult to traverse on with a vehicle. But maybe that's intentional. Don't be afraid to widen the map either, if necessary for more tank movement. The quickest route between the bases won't change.