These are what we call the 'YMMV items.' Things that some people find in this work. We call them 'your mileage might vary' because not everyone sees these things in the same way. This starts discussions in the trope lists, a thing we don't want. Please use the discussion page if you'd like to discuss any of these items.
Breather Level: The Entrance Hall, especially since it falls between the very difficult Ghost Ship and Time Device levels.
Fridge Logic: How did a guy who was such a wimp when he was alive suddenly become so good at fighting when he's revived as one of the undead?
Shame is an excellent fuel. Also, you can't kill a skeleton with an arrow to the eye.
There's nothing to say Dan was necessarily a wimp; he was the first one to get killed because he was one of the first to get involved in the battle.
For that matter, why isn't Dan under Zarok's control? Not being commanded by Palethorn during the sequel kind of makes sense, given that he almost certainly didn't have the 100+ years of experience with the spell book that Zarok had, but why didn't Dan come under Zarok's thrall like all the other zombies during the first game?
It seems like the implication was that Dan was sort of locked in-between worlds. Unable to truly pass on to his eternal reward because, well, he didn't earn it.
Nightmare Fuel: Humorous as the original game is, it still involves battling undead/demonic enemies. Special mention goes to the scarecrows.
The Sleeping Village level. The first half of the stage is populated with all the townsfolk turned insane due to Zarok's black magic. Which includes the children. A chunk of Dan's time will be spent running from axe-wielding, constantly-giggling girls.
That One Level: "The Ghost Ship" can seriously drive you crazy with its tricky jumps and unhelpful camera angles.