This is bothering me too much. Honestly, if you were to take out the sky and high poly terrain, it looks worse than a Halo CE map with a quick radiosity on it. The lighting is what makes maps shine. They should at least invest some time in real-time shadows for certain objects.
It would actually be cool (and suicide for your console) if they let you run lightmaps (not high quality ones) for forge maps.
Additionally, they could just make it so there's multiple lightmaps - one for the stock map, and one for the empty forge map.