you could program an 'almost' entire game as a plugin dll.
the current sdk (non-beta) is not complete, some features are missing and then you must use some c-script. and you need a starting script to open your dll.

the sdk beta (i hope it can become a release version soon) seems to be more complete, but i'm not sure if you could do an entire game whith it, whithout any c-script.
and whith the beta version, i believe you can create your own program and use the engine as a dll.