I'd really recommend giving Crimzon Clover a shot even on Novice, it was my first STG and it's just a quick blast.
Star Parodier is a good entry point as well with cute homages to Hudson's franchises.
GG Aleste and GG Aleste 2 are fantastic even on their super limited hardware.
Black Bird is a cool narrative-Fantasy Zone deal.
Deathsmiles was my first real STG and it's a great horishmup.
Neko Navy is a pretty basic doujin work but it gets the job done.

mushihimesama is both fairly beginner friendly + essential canon, and if you liked scarlet devil you can't really go wrong with the follow up game, perfect cherry blossom

judgement silversword always good too

Cycle Chaser H-5 is very beginner friendly and worth playing for the art and GEN/MD music
Blue Revolver's OST fuckin' bangs
Darius Gaiden is an artistic masterpiece, but you should also play with rapid-fire.
R-Type Delta has immaculate horror vibes in it's later stages
Gradius Interstellar Assault is a really cute exclusive to Game Boy that I think is better than most of the main entries.
Gate of Thunder has one of my favorite OSTs and kinda just rules in general
Steel Empire has a playable blimp and the world's hardest final boss
Gadget Twins fuckin' sucks

Start at the very beginning with SCRAMBLE, it's actually kind of sick

ight yeah this was a good call already since ive never heard of more than half of these, im already learning so much, who knew both the game gear and the wonderswan color secretly had kino

cotton 2 is the best shooting game. It has a certain toy-like sensibility to it that gives it more staying power than any other shooter I've played. No matter how many times you play it, even if it's been completely mastered, the playthrough will always come out different because you want to try something new. Honestly the game's flexibility makes other shooters look pedestrian by comparison, even the great ones. There's a confidence in all of its bizarre and strangely implemented systems that make it feel whole and fully featured, it isn't like other shooters where you're sometimes just going through the motions or repeating something you've already done. It's timeless, the loosey-goosey nonsensical world is a perfect match for a game with infinite possibilities. It's real good, you hear. When you're bored of the Battle Gareggas and Ketsuis, definitely play it.

The best of the normal shooting games is Thunder Force IV. I can't put it into words, it's a game where once you've played it you get it. Like, there's such energy and intensity to the action. Bullet hell-type shooters have their place but they've never come close to the excitement I feel with thunder force iv. It has probably the best soundtrack ever maybe. Just the other day I finished it on Hard and I feel like I'm on top of the world. It's the kind of game where, when it's all done and you're watching the credits roll, it truly feels like a great accomplishment. Like, I can do nothing for the next three weeks and I'll still feel accomplished.

There are plenty of other really great shooting games (all the Cave stuff, Battle Garegga, Ikaruga, etc) but none of them stack up to these two as far as I'm concerned.

more about thunder force iv: I think the bosses exemplify a lot of what makes it so great. I feel like in most shooters (especially bullet hell ones) bosses tend to feel like just different bullet patterns to avoid. In Thunder Force IV, they are real bosses, like in an action game. They are dynamic like an actual opponent, they make you think about how to attack them and move in ways that keep you on your toes. They exhilarating and sometimes exhausting, they stimulate your brain. They feel like real opponents. I will always like this more than a CAVE bullet hell boss

progear, one of the quintessential entrypoints into the genre imo. bursting with incredible artistry while still being easily readable on a gameplay level.

damn bein sold really hard on thunder force 4 off the bat here....buyin pretty hard on what im bein sold i feel too....

Seconded on thunder force iv, but forewarning it's real rough on a first play, there's a few fundamental shmup qol things it lacks that can make it seem overly-cheap or obtuse at first

Elsewise gotta give it up for the whole Darius series, but especially the console version of 2, gaiden and G-Darius

Apologies for my recommendations not being the best but I have a few
Battle Mania Daiginjou is my favorite shmup, has a lot of style and charm and it's pretty beginner friendly
Soldier Blade is a pretty great vertical shmup for the PC Engine.
Over Horizon is a very underlooked shmup on the Famicom, it's pretty solid and even let's you customize your options which is cool.
The later Twinbee games are pretty good. Ones like Detana, Pop'n, and Yahho. The bell system is a love it or hate it thing in this series but if you get used to it, it's a very cute and fun shmup series. The later ones also feature characters that were pretty popular in Japan when the series was going.
Xexex from Konami is a really good Arcade shmup. It can be challenging however it's really fun imo but one thing I would advise greatly is play the Japanese version, they made the game worse in other regions.

I can attest to darius gaiden being really good, but forewarning you it is damn hard. I'm not sure if this applies to the other versions but on the Saturn the continues are split between both players. However, you can just switch to the other controller port to use the second player's continues. Elevator Action Returns is another Saturn port from Taito which I think was originally on the same arcade hardware and it also has this. Weird. Anyways I'd recommend using that, at least to get accustomed to the game.

about Thunder Force IV, it has a port on the Saturn in the Thunder Force Gold Pack II compilation that's a bit better than the original. It pushes through the slowdown from the original (which wasn't a big problem), allows you to save your scores, and has a bonus mode that lets you play as the ship from thunder force III. I'd recommend playing this version. The Saturn has lots of really really good shooters so that's a good place to look if you're interested in games like this. I'm told that emulation can still be tricky but if you can get that going or if you own a saturn (which everybody should) that's the version to go with.

oh yeah that reminds me id meant to ask about playability for a good number of these, seeing as a lot of them are on wildly different hardware and if theres any that i would like, absolutely need to play one version over the other (also dreading having to possibly figure out how mame works and i dont want that weight on my shoulders)

@GutterTrash generally, you should just play the original. Look up if the home port of any given game is good, it so you can avoid MAME. There are some situations where playing a port is preferred (notably with Battle Garegga since the Saturn port and I imagine also the 2016 version add great features) but that's really on a game by game basis. I haven't dicked around with MAME a whole lot but I have a rom set for Final Burn on the Xbox that I just put on my new fangled "PC" and it works great with Final Burn Neo on Retroarch. I recommend using Retroarch with this stuff since it streamlines the process greatly. I'm not sure if I'm allowed to provide... links, so I'll just say that you should be good to go downloading a bios set for all consoles along with the newest MAME and Final Burn Neo core on Retroarch. You'll wanna reserve 15gb+ for a big rom set.

So I've always been in the same boat as you w/r/t knowing jack about shmups, so a few years ago I decided to just compile a list of every scrolling shooter ever and pursue an obviously doomed project to play and rank them in chronological release order (lol). I got about 50 in which covered everything right up to GRADIUS, which is more or less the biggest early turning point in the genre's development. So, all that to say that I can only speak authoritatively to the clunky, weird, dead-end ass prehistoric era (1981-1985). I would imagine that you don't have my particular kind of brain disease and therefore aren't at all interested in such a rigorous historical exercise, BUT if you did want a survey of the earliest genre origins, my favs were GUN.SMOKE, STINGER, GYRODINE, TWINBEE, EXED EXES, MEGA ZONE, and SPACE ODYSSEY. If not, feel free to disregard!

And to the playability question for those, I believe they are all Arcade originally, and MAME should be fine for all

rRootage Reloaded for Switch; it's a bunch of bite-sized danmaku challenges broken up into levels, and you can tackle them in any order. Each level takes about two minutes tops to complete, and is great for memorizing bullet patterns that are common in the genre. You can even switch the rules to a different shmup (Psyvariar, Giga Wing and Ikaruga) giving the game a ton of content.

Major strides have been made this day (i figured out how to operate retroarch)

I haven't played a Gradius I haven't liked, but Sexy Parodius is definitely the variant that I feel the most passionately in favour of.

@GutterTrash congratulations

Personally I think the Twinbee series is pretty begginer friendly, the SNES titles especially

oh yeah try to pace yourself out when playing all these games because filling your brain with shooter games might drive you insane

@HylianBran oh yeah obviously, i gave progear a good couple runthroughs the past couple days and tho i loved it i def was at least a bit overstimulated-feeling from it