First game in the series. A roguelike TPS boss rush where you add random bullshit to yourself to become stronger.
The second game in the series. A flight sim boss rush where you fight massive monsters in a jet, and need to fly close to them to gain defensive and offensive power.
The third and final game in the series. A roguelike TPS boss rush where you pick up objects katamari-style, which serves as both your attack and defense.