It's one of the mechanically most interesting 2d platformers of the 16 bit era, no simple jumping on enemies or shooting them. Freeze and break apart, with simple pellets or one of the so many special ammo types. Many worlds, each with new enemy types and environmental traps, lots of secrets too (secret levels and secret bosses as well). Toppled with wonderful pixelart graphics (the A1200 version was the prettiest, with bitmap backgrounds, not only a gradient like A500).
Pretty difficult to play, definitely requires some practice and a better controller map. The default 'up' for jump made it extra difficult, due to precision which is needed in some levels. When playing in an emulator I mapped 'up' to 'A' and 'fire' to 'X' which made it a lot more enjoyable.