First of all I'd like to get one thing straight: Your 3D work is pretty awesome
With that said, here's my thoughts on this:
In my opinion you have only two choices for this project: Doom3 or Source... I'd choose doom3 over source anytime...
Why? Because Source and similar engines are the last of it's generation. The old "build in editor, pre-render for hours" is a thing of the past. Future engines will use real time lightning just like the doom3 engine does today. The perfect thing with the doom3 engine is, that you can, just like with farcry, create stuff within the engine itself. No pre-rendering time. If you move a light, for example, you have instant feedback. One big drawback of the farcry engine is (and maybe that has changed, but I doubt it) it can only handle one real light on the screen at any time. There is a doom3 style level which demonstrates this pretty well (http://www.forum-3dcenter.de/vbullet...8&page=1&pp=20
it's german btw...).
It's also not true that the doom3 engine is only good for indoor stuff. Granted, it's been used only for that but future games will use it differently as the hardware starts to become even more powerful. Quake4 is also said to have large outdoor areas.
Which brings me to the next thing: multiplayer. It's true that doom3 suffers from a small modding and multiplayer comunity. But I think that's going to change when quake4 hits the market. Quake had and still has a strong community arround...
So if you like to bring your very good work to a game, without sacrificing too much eye candy, you have only one choice: Doom3
I'd personally start with just bringing your levels to the engine, so you can walk arround blood island in awesome 3d
When Quake4 hits the shelves, you can bring in multiplayer as well... Although let's face it: Such a mod would probably only have a small community of monkey geeks anyway
I hope this thing goes anywhere and doesn't die beeing only a good idea