Thanks for the replies everyone, I'm really glad to hear all of your thoughts! Before seeing any replies I was assuming that everyone would be asking for more action oriented combat, and I'm pleasantly surprised by the responses. I prototyped the Notrium combat style, and the melee really is the part where it fails. It should be slow enough for me to understand what's happening, but if I make it slow enough, the rest of the game starts feeling too slow. And I couldn't get over the fact that the keyboard movement controls are not suited to indoors, especially if any corridors are not perfectly angled.
I really did think a lot about having a good old turn based Fallout 1/2 combat system, but it's probably not the kind of gameplay I'm looking for. I'm hoping for a more fluid gameplay where the combats are something that don't stop you unless you want it to. I remember disliking easier opponents in Fallout precisely because it would take that halfa minute to move your character and get that single shot.
I'm inclined to move from the current system to strategic level fighting. I liked your thoughts ZeXLR8er, so I started off from there. My current thinking is something like this: