DOOM has amazing arenas that rely on spawn timers and triggers. Enemy placement is a big factor but the developers are seemingly afraid to have rooms start with higher demons already spawned. The only ones that kick into high gear from the start are the last arena from the last level (Argent Dnur), and the I am Vega level arenas. These are my favorites. In between fights there's more doom like enemy placement (like a pinky charging you in a small corridor with a soldier and hell razer behind it). For a sequel, expanding on the ideas from the original, I would fucking love to see a combination of the arenas presented and more classic enemy placement challenge rather than progressive spawning clusterfucks. Not that they aren't fun but it can be expanded upon for more difficulty and fun. The hardest arenas and the most fun imo combine platforming, jump pads, and enough demons on the map that you're forced to strafe though it all basically doing laps. At least thats what I found myself doing to win. All this only applies to nightmare, the game feels very different and more trivial on lower settings.
Basically I want more intricate arenas that rely on platforming and fast movement, more creative enemy placement and challenge, and of course bring on more Doom 2 enemies! Arachnoids are a must, maybe a lesser form of the Cyberdemon that we can fight with other demons spawned! They should use some WADS as inspiration, I became more passionate about the game trying to make shit in Snapmap. Learning that made me see how much better the game can be. For example, Wolfenstein TNO wasn't nearly as creative with its level design and enemy placement as The Old Blood was. TOB properly expanded on the ideas presented in TNO by making it harder in the right way. I just hope there WILL be a Doom 5 and they dont take another decade to make it so I can stop replaying this one.
Lastly, do away with the runes and suit upgrades. Not that theyre all bad (slow motion one is badass), but combined with mastered weapon mods it makes you very overpowered. Which would be fine if the demon count was raised and demanded such upgrades but that never happens. Either make the game really hard so we need the upgrades or rely more on the player skill over upgrades. I happen to like Glory Kills and minor cinematics, this is a modern doom reimagining, not Doom as it was in the 90s. Really loved this game, dunno about anyone else.