It's pretty good, if a pretty narrow game. I felt it was a little better before the dev made it easier, but it's still good and has some neat play and feel. They really should have made an option to play the original way as well as the easier way, but maybe they need to see some people buying it first. Things change from run-to-run, but after you get the characters unlocked, you don't have any roguelite style metaprogression to make it less arcade. Has two modes: the main adventure style mode, and a non-procedural time-limit score mode. There was talk of another mode coming ("gauntlet"), but haven't seen any sign of that for a while.
There are some other great proper twin-stick shmups in the sale, too. Devader is actually pretty fantastic and full of weird stuff--especially notable for the dev's great misinterpretation of bullet grazing, where you follow near to a bullet for a bit to absorb it and get a boost or trigger a secondary effect. I know some shmup fans hate slidey movement/momentum, so be warned Devader uses that. Then of course, there's Assault Android Cactus running its usual $5 sale price, which is crazy good, and Waves (and the unfinished Waves 2) always free now in memoriam of its dev. The tolerant may also enjoy the janky and under-polished XenoRaptor
and Touhou Endless Dream (much more a roguelite, with lots of upgrades and metaprogression, but still has that twin-stick feel).
And then there's space thruster style shooter Nova Drift, which has long been chugging away at early access, but is starting to talk of being ready for release after a couple more updates. Very upgrade heavy, but a neat game and we never get many thrusters.