Greetings,
Just finished the DOOM 2016 and while playing it, I got this idea (i'm pretty sure others have had it too) for a sequel.
Most of you will surely remember the Doom Slayer predecessors they showed at least a couple of times through the game (they had this sort of medieval templar-ish armor) and a mention of the original Doom Slayer who battled and defeated the Titan.
So, my idea for a sequel is to make it about the first Doom Slayer set in a medieval setting culminating in the defeat of the Titan and possible imprisonment of the DS.
Possible weapons could include things like:
blackpowder bomb (essentially a grenade, with a shrapnel upgrade)
a blunderbuss (very short range, but powerful cone spread = shotgun replacement)
a musket (powerful 1-shot and reload rifle)
Battle Axe / Claymore for powerful melee swings (maybe as a chainsaw replacement variant)
Dual Bastard Swords for faster chopping
and/or
Sword and Shield for blocking projectiles (upgrade could reflect projectiles back at the enemy?)
So there, just a little something of the top of my head. Feel free to add anything of your own if you come up with something and just general talking about a possible sequel.