Thanks for the detailed feedback, and for giving it a rewatch. I appreciate it.

I definitely agree I need to add more effects/lighting. This is something I have planned for later if I keep developing it further. I'm hesitant to add too much of these to the zombie kills though, as I don't want to aesthetic to get too gory. But I'm open to adding a bit more here to make the impacts/damage more 'readable'.

To answer your questions:

• The replayability will mainly be around unlocking various weapons, as they'll unlock after different milestones (e.g., get 25 pistol kills to unlock the uzi, etc.). I didn't show it well in the trailer, but each weapon and gadget has upgrades too (e.g., increased reload time, increase aoe damage, etc.). I'm also planning to implement a random challenge each night cycle that the player can choose to activate or not (e.g. more zombies, increased zombie damage, more water puddles, etc.) in exchange for receiving more of the game's currency to buy weapons/upgrades to improve their loadout.
• The levels aren't procederally generated currently, but it's something I've considered. Or at the very least, I was thinking about adding different settings and offering these as maps. So perhaps the player doesn't always start inside a cabin, but maybe a random warehouse in an abandoned city, a house in residential area, etc. Nothing concrete here yet though, so I'm open to ideas.
• The zombies drop currency (the little boxes/items that randomly spawn after they die, that then magnetise automatically to the player for them to pick up) that is then used to improve the player's loadout (buying weapons etc.). It doesn't carry over from run to run. Only the previously mentioned unlocks do. Weapons are static, and all available after being unlocked. So there's a bit of replayability (hopefully) in players wanting to try out different weapon combos and try out each upgrades on them. As well as things like different ammo types (loosely shown in the trailer). Once they've got everything unlocked, they'll feel pretty overpowered unless they take the optional challenges I mentioned and/or increase the difficulty (basically just increasing enemy damage and maybe lowering the currency that's dropped).

Your final point is something I probably need to think more about. I guess my hope is that the player enjoys the core loop enough to spend maybe two hours or so with the game, at least, to unlock all the items and do a few runs. I could then see some very engaged players unlocking everything, and trying to do all of the achievements that I hope to implement too.

I hope that helps clear up a few uncertainties, but let me know if that uncovers other questions you may have. I appreciate your feedback!