Warning Forever's gameplay is unlike most games, as the boss learns from you, rather than vise versa, makes it unique.
As bosses learn back from what you are learning, this is the reason why the gameplay is good. Even though there is a series of augmenting bosses starting at the most simplest and the unevolved Pure Heart, basically every time you play the game, the boss sequence is always different. And bosses actually learn from you, rather than which the boss sequence path is generated randomly. That means that if you violently destroy the boss's front part from the front, the next boss will have its front augmented with more segments and weapons, and than if you destroy the rear parts from the side, it forms a boss with a powerful front and a wide back. Eventually, it gets stronger and stronger and more armored and more armored as you progress 'til it reaches its devastating final form. If you try to do it by shooting the front part from the sides and destroy the rear parts' attached parts like weapons and additional sections, the boss will definitely transform with a heavily armored back and a wide front, proving how the boss learns from you. Eventually, for all possible paths, the difficulty gets so hard that it is almost impossible to fully destroy the boss (by destroying the core) within 30 seconds (each lost live costs means 20 seconds if set to normal mode) and/or without dying, making the next 8 or so bosses really hard, blocking your chance to reach fully evolved bosses.
The graphics are more old-school, but in overall it is very crisp and quite stunning. You can see how the boss is carefully designed and carefully aligned to suit each of its forms. Armored bosses eventually have one of the sides being rounded and compressed together while bosses designed for increased effectiveness of weapons have a very extended side or front/back. You also can see weapon and component effects as you can distinguish your and enemy weapons from fast, confusing-to-see vulcan shots to powerful thrusting missiles that home on to you. You can also see thruster and yellow shield effects that makes bosses more challenging and fun, but sadly graphics aren't antialiased and the boss stat radar is inaccurate sometimes, such as no defense stats in high-level bosses.
Sound is accurate and both realistic to fictional in Warning Forever. You are able to hear the clutching and booming of ships and weapons and the gasbursting and the funny futuristic shielding of bosses. Even though there is no music in this game, you actually can put any music you like by putting .ogg or .wav files in the Warning Forever folder, making Warning Forever more fun and exciting, especially if you put music suitable for shoot-em-up games.
Warning Forever in overall is a very good freeware game where bosses learn from you and grow up as you defeat them, and innovative weapons, ship design and the evaluation path technology makes Warning Forever so unique.