Twin stick shooters were arguably invented by 1984's Robotron but it was probably Geometry Wars that first succesfully mated the game type with home consoles, and so brought about the numerous titles that litter the genre today.
Geometry Wars and its sequel successfully merged the simplistic top-down gameplay (one stick moves your character, the other shoots in the direction you select - hence "twin stick" shooter) with killer presentation and enemy variety (and in Geometry Wars 2, gameplay modes) that kept it fresh and tight to play.
Death by Cube seeks to spice things up a bit, adding in some complexities that keep you thinking on your feet. The first of these is the dash - pulling in the left trigger causes you to move much faster, during which you're not only invulnerable and the enemy bullets cease tracking you, but you also stun any enemies you encounter. Shooting stunned enemies scores you a lot more points and combo opportunities, making it a powerful and important move to use.
The second significant innovation is the shield; pulling the right trigger encapsulates your character in a shield that prevents you being hit by enemy fire (but not by enemies themselves). You can also catch their bullets in your shield and will fire them out in the direction you're running when you release the shield button.
Mixing up the core gameplay (you can't shoot when you shield and you aim shielded shots with the left stick instead of the right, you can mix up shielding and dashing for extra complexity and effect) is where a lot of the difficulty comes in. It's actually quite complicated tracking multiple enemy types with multiple attack and defensive techniques simultaneously and Death by Cube doesn't waste levels holding your hand as you learn - the difficulty starts at 9 and ratchets up immediately to over 9,000. If you like frustration, pain and have spare controllers and TVs lying around in case of... accidents... this could be just the game for you.
There's a nifty character upgrade system, whereby you can earn the "chips" you earn by playing levels (also needed to unlock new levels) to buy new versions of your robot avatar. You select which of these robots you want to play with before starting a level, each of which has skills that are better suited to certain types of levels or play styles. There's the spreadshot guy, the back shot guy, the homing shot guy etc. You can also "level up" these skills (making your shots do more damage or adding more shots, etc) by picking up tokens in a level that are generated when you score combos.
Levels vary in type, from the "kill everything" to the "survive at all costs" types you'd expect from this type of game, with tiers of accomplishment awarding different levels of chips. This system works well, letting you advance (albeit at a slower pace) even if you're not good enough to earn the top awards in a given level.
The interface (the menu outside of the actual game) is horrible. The layout and information is presented in a confusing manner and it's never really clear what you're supposed to do or how you're supposed to do it. You'd think a novice developer would come up with something better than this by accident nine times out of ten, so to see an experienced publisher let something so abysmal through their net is confusing to say the least. Fortunately the actual functionality you're selecting is simple enough so you'll get the hang of it fairly quickly regardless.
Basically it's too hard, the gameplay mechanics unnecessarily complex and the strange exploding gore (you're shooting boxes and robots, where does all the blood and guts come from?) frequently obscures the too-fast action so much that you can't see what's going on anyway. Twin stick shooters are normally awesome - this one isn't. Avoid it unless you like extremely hard games or pretending things are good to just to annoy people.