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Spirit HD is a fun app with a trippy art style, developed by Jakyl. It combines interesting game play with neon colored enemies and environments to create an interesting experience.
It definitely bears an extremely strong resemblance to Geometry Wars, and by that, I mean the background grid and several of the enemies are blatantly lifted from one game to the other, but the game play is completely different, and a lot of fun.
By dragging your spirit around the screen, you must avoid enemies and create vortexes to swallow them up. When your spirit is moving a certain speed, it will leave a trail in its wake. By looping around and connecting the trail to itself, you create a vortex. You can choose to wrap enemies up or make smaller vortexes and lead them inside. There is a surprising amount of variety in the enemy types, and you'll often be forced to change up your strategy on the fly. The game comes complete with three different game modes.
Each mode is basically just a high score game, surviving as long as you can, racking up combos and points. In Classic mode, you basically do what I just described until you lose all of your lives. In Extreme mode, the enemies start off much stronger and come at you faster than Classic mode, but otherwise it's the same. Pulse mode is where things got really interesting. Rather than create your own vortexes, you have to collect these pulsing orbs, creating a vortex the instant you touch one. If the purple ring is small and inside the blue ring, you'll get a small vortex, but if it's expanded to the rim, you'll get a huge one. Any enemy that you kill leaves a coin, which you can collect to increase your score multiplier.
All three modes are a lot of fun to play, and the game as a whole is very well done. The neon, Technicolor art style works very well for this game. I especially love how the background is constantly changing color. You might as well be at a rave. The controls can take a bit of getting used to, and it seems way too easy to die at the speeds required to create vortexes. But with a little practice it becomes a lot of fun. This is a great game for only two dollars, and I recommend it.