Zanac (NES)
Like most bullet hell games, it is hard as shit, but this one is actually possible to do a full playthrough without dying once if you know what you're doing. It does have some typical cryptic NES bullshit going on though.
For example, in the first few seconds of the first stage, a lander ship will drop down. If you shoot it, a strange blue Pacman-ish pickup will appear. Instead of picking it up, shoot it a few times and it will turn red. The red pickup gives you an extra life and faster fire rate, whilst the blue one will only give you an extra life. Strangely, the pickup won't appear at all if you fire a missile before you shoot it with your cannon weapon. Now you know how to play the first 5 seconds of Zanac.
There are a ton of different pickups you can get, some good, some bad. If you are smart with them you can become near invincible. I am not sure about this, but Zanac may actually be the first game ever to have a dynamic difficulty setting that changes depending on player performance. Considering the game was made over 30 years ago, this is a pretty impressive achievement.
Rabi-Ribi (PC, PS4)
This is a pretty weird game. First of all, it is a kind of RPG platformer, yet also somehow a bullet hell game. It actually has a storyline too - you are a bunny that has been transformed into a bunnygirl. Completely bizarre, but surprisingly good gameplay. Can't really say too much about it because I'm not that far through the game yet, but there does seem to be a Metroidvania aspect to it as well.
Ikaruga (PC, Arcade, Multiple consoles)
Japanese vertical scroll shooter. It is fairly average except for one mechanic that sets it apart from other shooters. All the enemies you fight are black or white, and fire black or white projectiles. You can turn yourself either black or white, and if your colour matches a projectile, it will not harm you but the other colour will. It takes some getting used to, but I really like the puzzle aspect built on top of the fast paced shooting/movement part of the game.
1943 - Battle of Midway (Arcade, NES)
I played this game constantly as a kid on an arcade emulator. It has one of my favourite bits of video game music in it. The game isn't really that different to other shooters, but it just has a certain charm to it that I love, probably because I played it so much. It is actually one of the best NES arcade ports too, the game is basically the same.
You get a few different options to level up at the beginning of the game like attack, defence, special attack etc. These can be further improved by shooting specific ships and causing a weird red mountain thing to appear, which you fly into to bring up the upgrade screen. Not cryptic at all. Your health is "energy", which decreases at a constant rate, when you are hit or when you use your special attack. When it gets to 0, you will die instantly from one hit. The music changes when you drop below 20 energy and it gets tense as fuck, particularly if you made it a long way through the game. There is also 1942 as well, but it isn't as good as 1943.
Gradius and Salamander (Arcade, NES, multiple others)
Fuck both of these games. Salamander is an arcade spinoff of Gradius. The weapon pickup system is more basic, but the game is just unbelievably difficult. It has a sort of Space Invaders style destructible thing going on with some objects/scenery in the game too which is really impressive. Salamander is the Japanese one I think, it's called Life Force in the US, but I don't have that one.
Others worth listing
- Luftrausers
- Downwell
- Battle Garegga
- Touhou
- R-Type
R-Type is love, R-Type is life. I never played Rabi-Ribi, might have to check it out.
Bit Blaster XL is a pretty fun "casual" shmup on Steam for $0.99. It's pretty good for a couple hours here and there, definitely not super difficult by any means, but it's enjoyable.
If you want a much more casual, odd, story-driven shmup, check out the Princess Remedy series on Steam. It's another good way to spend 1-3 hours.