I was really enjoying it for a while. It's addictive and satisfying, and it gives you a lot of options with your weaponry and abilities that can really change things up significantly. I like the charm of the cheesy retro-futuristic themes and art style, and the music is great. It all has a kind of "budget" feel to it, but there's nothing wrong with the gameplay.
To advance through the game, you need to unlock medals, which you collect by completing certain tasks in each level. Subsequent levels are locked from you until you have collected enough medals to proceed, which means you'll need to replay these levels repetitively until you get more medals. The game is fun enough that this concept wasn't really a problem for me at first. I'd been happily replaying each level to unlock what I could, and then again in hardcore mode to unlock further medals... But then I got to Act III. The first chapter in Act III requires you to have 52 medals in order to play it. I had 40... I looked back over the medals I hadn't achieved, and I realised there's no way I could get anymore of them without hours of frustration. It was just beyond my skill level. Some of the objectives seem impossible to me, such as "Complete the level in under 25 seconds" when I don't even know how to reduce my time to 1 minute.
So the game is too unforgiving for my taste, and eventually it just lost me. If you're someone who plays a LOT of twin-stick shooters, and enjoys mastering each level in them, then I'm sure you'll love this. But if you're more like me, you have average skills, and you just want to experience the game without having to perfect everything, I'd give this one a miss.