The war is a lie
Frustratingly hard without the correct strategy. You will be scrambling your troops around the fortress as shells pound your fortress day and night. Your own guns will be struggling to fire before half of your firepower is blown to bits. The best strategy I found for the late game is to spam two or three Typhon MKIIIs with four to two ALASTOR MkIIIs with three flak defense towers. The config will rip through any fortress with ease, if you aim for the correct targets. For the early game, four to two ALASTORs, some ARCHONS, a couple of BASILISKs, and two or three flak towers will be enough. Remember: the war is a lie. Also, the universe is interesting, and I am sure many people either want a DLC or a new game as a sequel.