Not being a weapons mod fan myself, these kind of creations really need to be something special to get my attention. In the special case of Heretic - Order and Chaos, the coder amv2k9 exactly got what it needed. Order & Chaos' twist on Heretic's gameplay is such: You have entered a world where the very atmosphere itself slowly eats away at your health, and health pickups are extremely rare. All is not lost, though; your weapons siphon life from killed enemies, and your health maxes out at 500. Armor is also more plentiful; in fact, armor pickups ranging from a meagre 1 point to as many as 128 points now replace health artifacts and most powerups, and the max amount of armor you can have is 500. Doesn't sound interesting enough yet? Check the release and development thread over at ZDoom. It's definitely an interesting gameplay approach.