Game idea I had a brief inkling of trying to make before deciding to restrict myself to more attainable projects. The setting is a science-fantasyish thing where there is no FTL travel, instead portal generators are used to travel in between worlds. Something has gone wrong and you have to travel between worlds fighting hordes of enemies as you try to get to the next generator.
It controls like a twin stick shooter, you WASD to move and mouse to control where your character is aiming. There are a lot of enemies and they tend to try and close in on you, some have projectile attacks but they're slow enough to be dodged easily if there's only small numbers of enemies shooting at you. Each character has a 2-3 abilities that cost mana to use; for example there might be a jedi-esque character that pushes or pulls enemies, a character with suit of armor power armor with thrusters they can use to fly forwards or backwards, ect.
The way weapons work is a little unusual however. There are relatively few weapons, each with its own animations and detailed mechanics. Each weapon has a heavy and a light setting, so a pistol might shoot once if you hit LMB or three times rapid if you hit RMB, a melee weapon might have a jab and a bullet reflecting wide swing. Each comes with combos that you can chain together by alternating the different mouse buttons and pauses, as per a hack and slash game. Your character has a dodge roll and if you hold the mouse button down you can continue your combo after rolling. Each weapon has combos that will cause you to use one of your character's abilities at a reduced mana cost; that means that the combo will do something different depending on which character you have and certain weapons will be better in certain character's hands. So for example you might have a shotgun combo that would have the jedi character pull an enemy in and then shoot them at close range, but the armored character jump forward and do the same. And a third character might just do a ranged attack or a different ability and thus have less synergy with the shotgun.
Oh and has 4 player co-op. Hopefully that made sense, I'm tired.