Just want to post some resources that I've utilized and are Shmup related.
Some of these will be well known in the community, but if you're just starting out, then these might be of interest!
Guides:
Full Extent of the Jam - Anyone getting into the genre should definitely look over this.
Glossary - Terms Glossary. Very common terminology that is good to know.
Sternys Painless Progress Method - A way to track progress towards personal goals in the genre
Youtube Channels:
Shump Junkie - Reviews/lists of many shmups, more of overviews than in depth reviews.
The Electric Underground - More in depth reviews. He gets quite in depth, and while I don't always agree with his assessments, he's super passionate about the genre. Also hosts the Shmup Slam events.
Shooting Game Weekly - Each episode is about a specific game, showing super plays, with commentary. If you want to learn about a specific game and how to do scoring or survival, look through these archives. Not so much weekly anymore.
Jaimers - One of the best to ever do it. Lots of amazing clears on his channel. He does commentary via the yt captions.
Aktane - Commentary/Streamer
Icarus - Another streamer, makes guides, looks through obscure doujin stuff.
Pearl - Gameplay, some guides.
Others:
Restart Syndrome - Score tracker. Allows users to set category, upload replays, have a competitive leaderboard between members.
newStage - News feed specifically for STG and related genres. In Japanese, but automatic translation should work well enough.
Shmuplations - Lots of good interviews with developers.