This might be a big reply but i would like to share some insights about the campaign and why i agree with you on there, you don't need to read it if you want to.

"This mod is a fun way to spend an hour, but it just left me wanting more."
its not the first time i've heard that and can i understand it pretty well.

This campaign was planned to have a lot more (and be completely different, it wasnt exactly horror themed) but initially i was planning to split the work with a friend so we could focus what we do best in each area,
eventually this friend of mine gave up on hammer because of the headaches it gave her (understandable) and i didnt want to archive it and left it to rot there forever so i decided
to finish everything by myself and that ended up changing a lot of the campaign and its concept since i wanted to avoid things i am bad at (such as open areas, nature, displacements in general, etc) due to trying to keep a level of general quality,
due to that the campaign slowly moved in to a horror direction which reached a high point in map 3, and after many many weeks (if not over a month) just fixing rivers of bugs in map 3 i got very burned out and when it was the time to work on map 4 i was kinda lost and out of any good ideas on what to do on it (i wanted the horror to go more in a psychological route but i ended up going in a supernatural route, which got janky and went in to rework many times,
eventually turning in to the secret hard mode with extra tanks and i left the main route "normal").

At some point i ended up prioritizing primarily a more fluid L4D2 gameplay rather than something full on survival-horror (which is why you didnt had a frustrating time with these parts), i didnt scraped the original idea but made it so it wouldnt be frustrating or time consuming (and a bit too easy imo).

Also, to compensate my lack of detail in enviroment in general i focused on something more for the campaign, a lot of optional content and rewards for exploration, such as secret routes, alternative paths, tons of hidden stashes in all sorts of ways, some conceptual ideas ("readable" book in map 3), list goes on, something you dont usually see in campaigns and its a nice thing that i personally like.

At the end i didnt got disappointed with what i made, but i didnt got happy either, unironically i found someone to help me with the navmesh (which was one of the things that caused me way too many issues) only after the campaign was published, so a bit late to try and rework entire parts that i had to scrap since i couldnt make them work well :V

Im glad you had a good experience in overrall besides the expectation letdown

maybe one day i might make a sequel, a remake, a DC, i don't know, i would rather get better at hammer in general before trying out a big project like a campaign again

If you have anything more you would like to comment feel free to do so, i'll read everything

I always write my reviews for players first because most developers don't read them, but I'm glad you found the feedback useful regardless! Kudos for handling criticism well, not everyone does

I wish I could give you a detailed list of recommendations since you asked, but I'm unfortunately too busy with work right now. Still, here's the main takeaway:

There's a creative spark in your work that I liked seeing, and I hope you keep making stuff. Never be afraid of creating something unusual or strange -- that's what makes a work stand out.

(And if you just want to practice Hammer, smaller projects like survival maps or one-chapter campaigns are a good starting point!)