I guess for a shooter that isn't beatable, it doesn't make sense to wait until I beat it to review it, and I've played it for several hours already. This is just super great. In some ways it's just a very well done twin-stick shooter, which makes for a good game but doesn't really stand out by itself. It's polished, and all the fundamental mechanics feel and look and sound good. The things that really keep me coming back for a couple rounds every few days are the extra mechanics on top of the basic ones and the well thought out game modes (one in particular).
A slow motion ability is not exactly a new or unique concept, but it's used well in this game, with a limited meter for it that drains VERY quickly and recharges moderately quickly, so it's very often available, but only in small amounts. You also get bonus points while using it, so you have to decide whether to trade off using it to save your life or be risky and use it to pad combos for more points. The other main mechanic is the bomb system. Your combo multiplier goes up as you kill more enemies without a break of more than I think three seconds in between, and at certain multiples you're awarded a bomb, which as in most games insta-kills anything in a relatively large radius around you. However, unlike most games, you cannot save it for later use. You have a few seconds to activate it, or it's gone forever. If timed/chained properly though, you can use a bomb to get you a good chunk of the way to your next bomb, then repeat. Of course, when there are enough things on the screen that you can get away with that, you need to be on your toes or you won't last long.
It has some common game modes like unlimited time with a limited number of lives, or infinite lives but a fixed amount of playtime, and some more exotic or panic-inducing ones like the one which lights up a small spot on the screen, and if you don't move to it within a few seconds you die. Once you get there, it picks a new random location. Oh, and you also have to keep playing the normal game while doing that. Good luck. The one I've really gotten stuck on is Bombing Run, which takes away your guns entirely but continues to spawn enemies. It places a bomb pad at a random location where you can pick up a bomb, at which point it creates a delivery point at a different random location. When you bring the bomb there, it detonates like a bomb in the other normal modes, and a new bomb pad is generated. If you get a high enough combo, you can get a single-use defensive shield, but mostly it's about positioning, movement, and reading patterns and paths through what becomes a huge, chaotic mess at higher levels. It's really great for practicing that stuff without being distracted by all the shooting you're normally doing in most modes of most games, and it's just plain fun.