Firstly, simple is good. While detail is nice, if it doesn't help your gameplay, you really shouldn't be using much of it. Of course, if your map is plain, a little detail here and there is awesome. This map works well without it, in my opinion. I love the theme you've got constructed.
On the other hand, you ring placement needs a bit of work. You want your rings in the midle, where everybody can hget them wihout trying to cram themselves against the wall and being an easier target. I got most of my rings in the map through the ringboxes on the pillars and in the middle of the map.
And, uh, I don't know what to say about the under-water area. I don't like jumping on the steps much, so make the jumps a little easier next time.
And on a technical note, I noticed you're solving the colormap issue by using a water block both above above and below the FOF. I'd suggest you just place the FOF directly inside the water block, and tag the colormap to the FOF's control sector. The FOF will just use the colormap in it's shadow, and it'll be fine.
