Great Old One
never did see that one. The Battlesystem 2E one wasn't too bad, it kept everything flowing pretty smoothly (unlike the 1E version).
My main problem with the Battlesystem is that it uses miniatures with a set scale, and it's hard to represent really large armies with it, it does not scale properly. I't also absolutely dependent on a map and is really a wargame in its own right.
The War Machine is completely different, it's both much simpler in the sense that you don't need a map or figurines, it can be TotM, and it scales really well, you can manage any sort of army. The tactics are also cool and leave a large place to intervention by the PCs, in terms of spying or taking out leaders. It makes it much easier to blend with more standard D&D adventures.