A few thoughts come to mind re enemy challenge without having to make them tanky:
Adding minimal assets
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Have the drone enemy dash between a set of checkpoints, and only fire from a checkpoint (maybe use a particle effect to indicate a dash jet/rocket?). Makes it harder for the player to hit them.
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Give turrets a windup sound and period, Then place them tucked behind door corners, like Symmetra tends to place her turrets in Overwatch. That’ll catch players off guard, but give them a chance to react
More effort, needing more assets
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Have a drone variant the flies at a high altitude and drops bombs. Use it to harras players in rooms that have a lot of turrets (after having introduced them)
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Add some enemies that don’t shoot, but move quickly and get intnehnway Metroid Prime has bats that fly circuits that get in the way of some platforming you need to do, but don’t attack you directly, for example.
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Add enemies that do suicide attacks.
Misc
I also think giving the player shots a faster travel time (and a quicker reload time, I think) would help make the increased movement and angles more, though that takes it away from Doom and moves it towards Metroid Prime some.
Aiming and movement are parts of the challenge of an FPS as well, and are more interesting to interact with than just shooting something 5 times.
Granted, these are ideas in retrospect, and I don’t know what sort of time you’d have had to implement them during the jam, heh. Like I said before, getting 3D done during the jam at all is impressive.