Starward Rogue is a roguelite shoot em up, kinda like The Binding of Isaac or Enter the Gungeon, only more directly inspired by Japanese shoot 'em ups, which is made evident by the colorful bullet patterns and Tohou being directly mentioned in the highest difficulty setting.
In that sense, I'd say it's pretty good. The action is fast paced, there are plenty of interesting upgrades and the presentation is generally good. There's no story or anything like that, but the game comes with 9 different playable mechs for some added replay value.
However, I'd say the game is not good enough to warrant a significant time investment, some key nuances of shoot 'em up design are missing, the most important among them being sufficient sound cues and a way to easily distinguish the player's projectiles from enemy ones. Obviously, the bullet curtains look prettier this way, but they are also much harder to read.
In short, I think Starward Rogue isn't half bad for a few runs. You probably won't get 100 hours out of it, but that's fine, not every game needs to be like a second job.