I think this is an overall excellent entry, and it is because it's better than most that I wanted to critique some finer game design points:
I think that the idea of spending blood to open doors works on paper, but in practice, when presented with two or more opaque doors, there's no real choice to be made, because there's no information to make an informed decision with. You either choose one or another. So if your choice actually matters (i.e., it's important to open one and not the other), it becomes frustrating because the player is punished with a removal of blood over a choice that can only be made via trial and error.
To compensate for this, you guys added lots of blood packs so that you could never really run out of blood. However, that also invalidates the game mechanic itself, since at that point, you're not really sacrificing anything of value if you can just refill blood from a million different places, so blood just becomes a resource you have to tediously manage, much like stamina. If you use too much (and you have to), you are obliged to sit around refilling it from a blood pack for a while.
So you've designed yourself into a hole with the blood mechanic because if you place too little, it's frustrating and you get stuck, and if you place too much, it's too easy, with virtually no middle ground.
I would recommend solving this by making bloodpacks scarce while also making sure that there's intelligent ways to manage blood. That can be as simple as making the doors have grates that you can peek through. That way, you can make an informed decision as to whether or not you want to open that door at all. For instance, maybe the door leads to a hallway full of other doors, but you see a bloodpack on the wall, so it's a low-risk door. Or maybe you see no bloodpack, but there's a pentagram shrine, so you'll come back to that once you're sure you have enough blood to spare.
Maybe blood could even come back / regenerate, but it happens slowly. So if you ever really mess up and run completely out of blood packs, you can sit around and wait for it to come back--except you can't sit in one spot because the patrolling enemies will eventually get you. In that way, blood could be like fuel. With it, you can move quickly, open any door you please, and feel rewarded for your wits and budgeting. Without it, you're a coward, hiding in closets and hoping the enemies don't clobber you while you're trying to regain enough blood to open that door that you should have opened earlier.
An additional way to make blood scarce without making it completely frustrating is to put some bloodpacks in easy-to-reach places, while placing others in rooms full of enemies or other difficult challenges. That way, it's not just "oops, that was the last bloodpack", but rather "okay, this is the last bloodpack, except for that stash in the basement I read about.... I don't want to go down there, but I don't have any other choice." This way, you can punish the player gradually for mis-managing blood, with each punishment becoming more severe than the last, by sending him into riskier and riskier areas to get the remaining blood.
Lastly, I wanted to comment on the big dudes. They seem unkillable, which is fine, but there appears to be no way to break the chase and hide from them, and stunning them with blood doesn't last very long. I think if the blood stunned them for longer, like 1-2 seconds, and they stopped chasing and started searching for the player once line of sight has been broken, it would be much better. As it was, I was killed because I couldn't loop the evil dude around the hallways long enough to crank the portcullis open, and quickly gave up on trying to stun him with blood since throwing blood at him slowed both of us down, not allowing me to gain any real distance over him.
Anyway all that aside, this is a great entry! I think overall it's got some promise if you wanted to do a post-LD version.