What's the difference between this and regular rampart?
I'll just say that I absolutely loved the original Rampant, and I still think it's a great addition. But, I had built my base up for dealing with max strength Rampant enemies, and as long as I had access to the more advanced weapons in mods like Rampant Arsenal, it didn't end up being a big challenge after a while. Fun, but not especially hard once you figured out how to deal.
When I switched it over to Rampant Fixed, though, I noticed that the hit points were significantly lower and the enemies much easier to kill (presumably the HP scaling didn't work the same?). But no matter, they destroyed me anyway. They moved faster, attacked in more mixed groups, and probed defenses more aggressively. They were quicker to abandon points where they weren't making much progress. Even simple things like the spawner biters spawning their little devil children outside the range of my weapons made them extremely dangerous.
The worst was the underground attacks, though. Once they started probing areas of me base with random underground attacks under lakes, I lost huge sections of my base and had to reevaluate how I defended in those areas. The underground groups weren't as big or dangerous, but if you aren't prepared for them they can completely ruin you. And once they are successful in an area they are very very aggresive at attacking that area again until you start fending them off.
All in all, it is fantastic. It actually makes me want to mod the game myself to turn it more into an RTS style game that focuses primarily on combat.