I don't know what a lower-detailed version would look like 🤔. Cute?
For music all I could think of was 8-bit Duke Nukem theme. There are some great ones on youtube. They sound awesome while playing Slaughter.
The new 'ghost' effect on enemies is neat. I can't tell sometimes if they're going in the walls or are just transparent. Maybe both?
I think cleaning up the edges of cliffs would do a lot to reduce the visual confusion if that's possible. Maybe a few small tweaks and suddenly everyone can play it.
I like the 1st new level, level 4 with the red/yellow/blue. That's when I noticed the ghost effect. In the new level 7 the destructible portals is a neat idea that stumped me for a bit- I mean, there was nothing else to do right? Cool mechanic. AAAND it finally clicked how to beat the game in level 9. Duh! 🤦♂️But I got overwhelmed with all the red on red and close quarter enemies and the menu text was black making it pretty hard to read.
I think I realized part of why the new level 7 felt off. You go from the open blue/yellow level, to Hell basically, and then back into the trees with level 8. With a name like Slaughter the red/darker levels totally makes sense but they're mixed in with the rest. You could start the game off in the overworld, more open/brighter levels like 1,2,3, 8 and 9 and then proceed to take a trip into Hell with the darker ones like 4,5,7. Maybe make it something like 1,2,8,3,9,4,5,7. But lvl 9 is waaay too hard to go in the middle. it's honestly an incredible end-cap to the game sooo... man idk lol.
If you feel it's time for you to move on for now that's probably for the best. I'm an NES dweeb (still 6502 so yay).
Still, I can't help imagining all sorts of things for this, like new or reimagined games in the Slaughter engine. There hasn't been an FPS that's run at this speed before for the NES. An FPS RPG like a Zelda 1 or Crystalis would be insane. Bomberman. Also just fleshing this game out would, for myself, be equal to Former Dawn. Pack a manual with enemy names and behavior, level names and settings, a storyline (you're here to kick ass and chew bubble gum?). Snes controller integration could give shoulder buttons for strafing and added buttons for easier weapon swapping/bombs. Saves would be nice but it's a pretty short game and skippable levels (Give Up) and Memory/Recall make up for it.