@nogc is still a new addition to the language and phobos is not fully flagged with it.
D devs are working on a solution to reduce gc dependence, it's just not quite there yet.
There are gc-less stdlibs here if you want to avoid phobos: http://wiki.dlang.org/Libraries_and_Frameworks#Alternative_s...
For game programming you should consider data oriented design. It really helps avoid the gc and makes your code faster and (imo) simpler.
Btw: http://forum.dlang.org/ is a great place to learn about ongoing development or to ask questions.
> Stopping all other threads than the thread currently trying to allocate GC memory
This doesn't need to be the case, and is one of the strengths of garbage collected languages, IMO. Garbage collection can be performed by another cpu asynchronously, essentially making it free.
For game programming you should consider data oriented design. It really helps avoid the gc and makes your code faster and (imo) simpler.
Btw: http://forum.dlang.org/ is a great place to learn about ongoing development or to ask questions.