psi circuit, to release a circle shock wave of destruction. Sometimes there are boss fights.
When the enemies are slain, you collect the crystals that they dropped. These can be used to upgrade the speed with which your weapon charges, to decrease it's cool-down time or to strengthen your shield (yes, you have a self-recharging psi shield thingey). Other than the purchasable upgrades, there are free upgrades and permanent bonus-giving artifacts to be found in treasure chests after boss battles.
The impression of the game on me is a very positive one. It has a cyberwizard/cyberpunk style and uses color of the environment and different music to convey information: the redness of the surrounding indicates the danger (amount of enemies) and the music lets you know what part of the map you are currently in. The music palette consists of various funky and/or chill chiptunes.
Also please be warned: because of the addicting attitude of this game, I went to bed at four in the morning yesterday..