Not sure why people are calling the game unplayable or barely playable tbh. Its got exactly the same controls bar one difference(medkits) from the first game. Arrow keys to move, left mouse to attack, right mouse for special, tab and mouse click to use meds or change characters. At the same time, the only real differences in gameplay from the first game are:
Some stages require all monsters to die to progress.
Boulders are replaced with green orbs
Purple crystals are replaced with purple orbs
Medkits are a thing.
This game is just like the first, ridiculously easy even without the power crystal(in the ship) cheat for 10x hp and power. The only annoying thing is getting the true ending which requires hunting down all 10 purple orbs in levels, seeing all service h scenes(5 for secretaries from first game, 5 for the girls in this game) etc. Even then, the download comes with a 100% save file already and pressing the second last option on the main menu is the gallery where you can see everything.