The theme has a beautiful atmosphere, it fits the setting really well. Futuristic and swampy at the same time - not easy to balance, but you did a great job.
Also, nice use of filters.
If anything, I'd give the drums a bit more variation instead of just fading them in and out. And if you want to build up more tension, some high pitched strings or synth sounds far in the background might help.

If anything, I'd give the drums a bit more variation instead of just fading them in and out. And if you want to build up more tension, some high pitched strings or synth sounds far in the background might help.