Although I'm a huge fan of the earliest arcade shooting games (Defender/Stargate, Asteroids, etc.) there are a class of mid-1980's shooters from Japan that raised the bar in terms of shooter difficulty, which caught me by surprise.
(UFO Robo Dangar by Nichibutsu 1986)
By the early to mid-1990's shooters evolved into bullet hell style shumps with a seemingly impossible barrage to doge and shoot back against, but somehow managed to allow players to slip by with a feeling of god like abilities. The truth is, while these later shmups added a ton more bullets/sprites on screen, pushing arcade hardware to its maximum, they also greatly simplified enemy movement and patterns, while reducing hitboxes and even allowing some laziness to collision detection routines. These bullet hell style games are what I've been primarily playing for the last 10 years or so. So going back to play earlier shooters, with a seemingly simpler challenge of smaller number of bullets and enemies on screen, and having my butt handed to me, is not only frustrating, but is down right ego busting.
Let me take UFO Robo Dangar as an example. With a low number of on screen bullets and sprites, difficulty is primarily centered around enemy movements. Enemies are able to accelerate up to 2x your player ship's speed, and literally run rings around you. Enemies are also able to run off the sides or bottom of the screen and loop right back onto the screen if not killed, most times accelerating to kamikaze into you if they get behind you. Enemies are free to fire upon you at any range, making point blank shots a common occurrence. These tactics would be considered cheap or down right bad programming by today's shmup standards, but is the genesis of the genra in terms of difficulty.
Anyway, I have a greater respect for shmup players of the mid-80s, and I can now see why the gen
ra evolved as it did, attracting new players and making them feel a greater accomplishment when it comes to the challenge of difficulty. I can also now see why Dangar implemented a butt shield powerup. :)
