Hi there,
my idea about UT theme is one big building with a "garden" in its center with one huge and few regular trees, maybe some little lake with waterfall, a bunker or other kind of army structure and some sewerage-like close-combat spaces. Player could use 4 elevators to reach top of the structure and also inside of central tree could be an elevator. I think that concept like this might provide long, medium and close distance opportunities with interesting terrain.
WIP images:
I did not created this picture, but I have something like that in my mind:
Sorry for my bad English.
Replies
Green forests are definitely pretty to look at, but the only thing you have to be careful of would be visual clarity. Your bottom picture for instance has too much clutter and the players would never stand out against the green bushes everywhere. That along with the seemingly flat rolling hills doesn't lead well for a twitch-fps arena shooter like Unreal Tournament. However, if they bring back Onslaught I could easily see the more wide open landscape like in your rough 3D shots being used. Even in ONS though the level layout was almost never just as flat as your shots so what you need is more variety in your areas.
I'd suggest try to focus on the areas of interest you described like the central tree, which sounds big enough to fight on top of the branches ( You said there's an elevator inside the tree )
Here's an idea. You could move away from one central chunk of land and try a sci-fi take at leveled gardens or greenhouses. Look at utopian architecture and try to put some more landmarks and points of interest besides the central giant tree. Possibly mix it up having some outdoor and indoor things. Just because it's one giant greenhouse doesn't mean there couldn't be self-contained smaller greenhouses of different habitats or alien environments.
It could be cool to be able to platform on top of smaller greenhouses connecting the areas around as well as inside them giving some interest to the player to be able to see the others above/below but can't interact directly with them at that point. Another map in Unreal Tournament has barely touched on this territory of glass-floors and ceilings but it would be more interesting if it wasnt always indoors like in Coret https://www.google.com/#q=Unreal+tournament+Coret
Some ref to get the gears turning.
https://www.google.com/search?q=Sci+Fi+garden&source=lnms&tbm=isch&sa=X&ei=hlHXU9mfLYKbyATHjoJw&ved=0CAYQ_AUoAQ&biw=2144&bih=1068&dpr=0.9#imgdii=_
https://www.google.com/search?q=Layered+garden&source=lnms&tbm=isch&sa=X&ei=JFLXU8nLBsqpyASB54KADg&ved=0CAYQ_AUoAQ&biw=2144&bih=1068&dpr=0.9#q=Stacked+garden&tbm=isch&imgdii=_
http://inhabitat.com/eden-project-giant-bubble-biomes-are-worlds-largest-greenhouse/eden-project-lead/?extend=1
https://www.google.com/search?q=sci+fi+greenhouse&source=lnms&tbm=isch&sa=X&ei=elnXU7igDMGZyASMkoH4Bg&ved=0CAYQ_AUoAQ&biw=2144&bih=1068&dpr=0.9#imgdii=_
https://www.google.com/search?q=geodesic+greenhouse&client=firefox-a&hs=gmj&rls=org.mozilla:en-US:official&channel=rcs&source=lnms&tbm=isch&sa=X&ei=rlnXU6LvM8KpyATuqYGgDw&ved=0CAcQ_AUoAg&biw=2144&bih=1068&dpr=0.9#channel=rcs&q=sci+fi+utopia&rls=org.mozilla:en-US:official&tbm=isch&imgdii=_
https://www.google.com/search?q=sci+fi+greenhouse&source=lnms&tbm=isch&sa=X&ei=elnXU7igDMGZyASMkoH4Bg&ved=0CAYQ_AUoAQ&biw=2144&bih=1068&dpr=0.9#q=green%20city%20future&revid=1788006471&tbm=isch&imgdii=_
http://www.kuriositas.com/2011/05/geodesic-magic-theres-no-place-like.html
https://www.google.com/search?channel=rcs&q=lunar+greenhouse&rls=org.mozilla:en-US:official&tbm=isch&ei=r1nXU8qAOcW0yASUlYDADA
https://www.google.com/search?q=geodesic+greenhouse&client=firefox-a&hs=gmj&rls=org.mozilla:en-US:official&channel=rcs&source=lnms&tbm=isch&sa=X&ei=rlnXU6LvM8KpyATuqYGgDw&ved=0CAcQ_AUoAg&biw=2144&bih=1068&dpr=0.9#channel=rcs&q=greenhouse+on+mars&rls=org.mozilla:en-US:official&tbm=isch&imgdii=_
https://www.google.com/search?q=Layered+garden&source=lnms&tbm=isch&sa=X&ei=JFLXU8nLBsqpyASB54KADg&ved=0CAYQ_AUoAQ&biw=2144&bih=1068&dpr=0.9#q=Stacked+garden&tbm=isch&imgdii=
http://www.thomasdoyle.net/bearings/