If you like shmups but don't like the idea of having to play all stages in one sitting and want something with a more moderate difficulty try Ginga Force and Natsuki Chronicles if you haven't already.
https://www.youtube.com/watch?v=-xHriMqMxPM
https://www.youtube.com/watch?v=orchqNVEoFU

Also Drainus, which is a very good choice for beginners.
https://www.youtube.com/watch?v=jhNCDYt4fAc