Figured I'd share this considering what I'm encountering right now.

I added a bunch of movement tech to my Downwell clone with kicking off enemies, pushing off walls to go faster further down, etc.

Please be aware if you have a bunch of speed in your game, then players will travel across the map too quick. I have an idea to fix this but yeah learning this the hard way is a big oof. I'm not saying throttle the speed of your game, by all means but speed will affect how big you make the map.

The other problem is slowing down the game makes it boring and feel sluggish so that's out the window.

Rather than increase the speed, how about increasing the illusion of speed? I haven't tried these out, but perhaps zooming in (or otherwise reducing the vertical and/or horizontal fov, e.g with black bars), moving the camera behind the player (rather than centering the camera on the character), motion blur/artifacts and colour shifting could probably help make players feel like they're travelling faster (after adding a slight speed boost).