If I knew C++ you can bet I'd be modifying the engine I am using which is free and open source and the license is very clear on that.
I can only use the Lua scripting right now, but when I buckle down and apply myself to learn C++ this is the engine I will be using. It is called Maratis 3D.
As for your screenshot, I actually do think that such a look is very capable in Maratis, although it doesn't offer a lot of tools to help make it easier (you'd have to make it yourself.) I have to bake in my color and ambient occlusion before I enter Maratis.
To get the water to look like that you could use an animated normal map (which I have yet to do in Maratis, although I have done animated textures to make water).
Someone has also simulated fog in Maratis. As for the buildings I would use Google Sketchup (this is my software of choice hands down when it comes to environment modeling). My main hang up is all the time it takes to texture all the buildings (although I am finding a workflow for doing such a thing.)
Here is a link to my showcase on what technical things I was able to do with Maratis:
I also have other posts on the site as well with more photos.