This is crazy. Were you meant to just run from some fights, because I can't see how you can beat all enemies. Not with his health and ammo capacity. The last fight I just ran to the exit.

yes, IIRC, that annoyed the hell out of me too.

These levels are pretty fun, but suffer from some severe balance issues. Next one, Spooky Mansion, starts really tough, because you run out of ammo soon. I had to restart and make sure I kill the zombies with a knife. Then after getting the shotgun it becomes very easy. Eeasy enemies compared to previous one. But... there is only one life seed in the whole level. Hidden at the very beginning. Not such a problem in itself, since it's fairly easy, but you should be aware of it. A player might say, "So I've got only 10 health left. Not a problem I'll probably find health soon." and be in for a nastsy surprise when he gets to fight the slightly tougher monsters at the end. Doable, but not pleasant.

It's like these levels weren't tested properly by players who do not know what the level will bring and expect normal ammo/health amounts.

Yeah, the JoJo level was easily the hardest in NL... I'd beaten it by using the Flayer and the alt-mode of the Orb whenever I could. The end fight isn't bad, though, all you have to do is approach the monsters than retreat as soon as one of them begins its area attack. It will damage the others, and after that, they'll completely ignore you and turn on each other. You just have to wait till thay're weakened or dead than finish the survivor(s) with the Flayer.