I'm too young to remember its initial impact on the world, but like many I'm fully aware of its legendary status, and have played its genius on many occasions. Space Invaders threw the gamer into a stylised future, vaguely reminiscent of Star Wars. No previous experience was necessary; and any player could quickly jump in and cause as much destruction as possible.
The would-be pilot started with three lives and had to move his/her ship from left to right along the bottom of the screen, whilst using the shields provided to, in effect, hide and shoot as you brought down wave after wave of Invaders. The aliens started slowly, but with each take-down they descended ever closer, and became aggressively faster. Bonus points were awarded for taking out the Invaders in a certain order; and large UFO's would often fly across the top of the screen, giving the gamer the chance to score big if they nailed it. Many tactics worked, and a favourite of mine was to clear the lower row and middle section immediately, which dramatically increased your chances of progressing further, and increasing your score.
The trend continued, and many more shoot-em-ups arrived... Asteroids, Defender and Galaxians all proved popular, and for a while were considered some of the best games on the planet. In fact, the genre enjoyed nearly two decades of blasting, but sadly declined somewhat with the demise of 2D in favour of 3D. These days, it appears as if all the best shoot-em-ups came out years ago, with maybe only the bullet hell of Ikuruga standing firm as the last great bastion for the genre. Maybe there are others, but back in the day shooters ruled, and shoot-em-ups were notorious for really pushing the systems hardware. Can the same be said for the likes of Pixel Junk Shooter, or any shoot-em-up of this generation of consoles?
In my opinion, the real cause of shoot-em-ups decline in popularity is that they need mastering, and in today's world with so many other distractions, time is something a lot of people simply can't give, and so gamers go for the easier option. But for those of us that don't yet have their own spaceship, and would simply like to fly through space with a laser guided missile strapped to their backs, however niche... will always long for a shoot-em-up.
The most crucial space battles:
Thunder Force IV
Weapons That Changed the World
A living breathing weapon that can attach to the front or rear of the R9 fighter, delivering all kinds of nastiness.
known to many as the Beam, a weapon for all occasions, and any situation. No matter the enemy, once the beam has built up to maximum, it'll rip right through anything.
Gradius / Nemesis: Power meter
This is more of a holster, for every type of weapon available. Selectable weapons ranged from a missile weapon, laser, and double weapons.
ThunderForce IV: The Thunder Sword
This fantastic weapon must be seen to be believed. Let the energy build up in the ships core, then press the fire button to release a colossal burst of energy.
Radiant Silvergun: Radiant Sword
A polygonal sword that can deal heavy damage up close. As soon as the button is pressed it swings in a full circle around the craft
Ikaruga: Twin polarity
The twin polarity concept in Ikaruga changed the way we play shoot-em-ups forever... instead of trying to dodge enemy fire, switch polarity to the same colour of the enemies gun fire and absorb it as energy.