I also personally like this system, but don't use it. While it adds realism to combat injuries, it's a system more detrimental to the PCs. Yes, it affects the baddies, but they're not alive along enough with that penalty through multiple rounds (well, maybe except the boss). And it's particularly brutal if the PCs don't have a dedicated healer during combat.
We decided to run a one-shot with a number of variant rules we all had wanted to try out... Wound Threshholds had an interesting effect. On the one hand, it did a good job of representing fatigue from battle. But my players weren't thrilled with all of the extra numbers they had to keep track of. it was hard to tell if players were remembering to use the penalties or not - and so the number of times we had to verify, or adjust the numbers really slowed down combat. My players were convinced that penalties also made combat take more rounds, due to the compounding effects of them losing precision, lowering their own ac thereby them taking more damage, and needing more in combat healing.
Its possible that with prolonged use, it wouldn't make it feel like such a slog, but on the other hand -it seems like the slog of a long drawn out battle is sort of the point.