Cactus is a top-down twinstick shooter where you have to overcome waves of robot enemies, and keep the Battery from running out before the level ends.
The game in one picture (for controller users, anyway)
For KBM users: move with WASD, aim with the mouse, fire with left click, weapon swap with right click or space.
Health: Your health. You can take 5 regular hits (eg. small bullets) without getting knocked down. Your health will automatically regenerate if you don't take damage for 5 seconds.
Weapon power: How strong your primary weapon is (your secondary never changes). You start at 0 stars and gain a star every time you fill the bar, to a maximum of 3 stars. Collect Volts from enemies to upgrade it.
Current weapon indicator: Tells you if you are using your primary or secondary weapon.
Battery: Your current battery level, which is slowly draining. You will fail the level if you run out of Battery. Kill enemies and pick up Batteries to top it up.
Combo chain length: Killing enemies quickly in succession lets you build up a combo for more points. This tells you how long the combo is, as well as how much time you have to kill the next enemy.
Combo multiplier: Tells you the score bonus based on combo chain length. Maxes out at 10x.
Score: Your current level score, based on collecting the Battery, killing mobs, getting combos, and not getting knocked down. You also get a time bonus at the end of the level.
Beyond the Basics
See Mechanics for more information.