Sine Mora is a bullet-hell game. At first, it doesn't seem like a proper bullet-hell since it doesn't seem as frantic or flood the screen with bullets. As you progress, the intensity does ramp up, but it still doesn't feel as hardcore as some other games like Ikaruga. However, even though the Story mode had 2 difficulty levels, you can play Arcade mode where two more difficulties are available. This is where things get really tough and is only for the hardcore.
The game scrolls horizontally, and you move with the directional arrows and use three buttons; A,S and D. S shoots bullets, D slows down time, and A uses your secondary attack. Secondary attack is a powerful but limited use weapon, where the pilot dictates which attack you have. During the first third of the game, it doesn't seem necessary to slow down time, but it becomes useful later on when plenty of bullets will be on-screen. Using this mechanic depletes a gauge which can be recovered by picking up the power-ups that enemies can drop.
When you get hit, you lose time, and when the timer reaches zero; you lose a life. You can recover time by destroying enemies, and your time is fully replenished when you complete a section. Additionally, when you are hit, you drop your weapon power-ups so your attacks then become weaker. You can quickly scramble to pick them back up, but you may need to slow down time in order to dodge the bullets and reach them.
Another interesting thing about Sine Mora, is that it is very story-driven. This seems to hinder the game since it seems to stop you constantly to give you more dialog, and you find yourself holding space-bar to speed up the cut-scenes to get back into the action. The story is really hard to follow, especially since you alternate between two sides. Arcade mode allows you to play the levels uninterrupted.
There are plenty of huge bosses to fight. There's a separate Boss Training mode where you can practice taking them down on various difficulties and different plane/pilot/power-up combinations of your choice.
At first, I found Sine Mora quite boring, but the more I played, the more I enjoyed it. I found it quite frustrating that the difficulty jump between Challenging (2nd difficulty) and Hardcore (3rd difficulty) seemed too great. You didn't seem to have much time, and the penalty for being hit was too great.
In the end, I found Sine Mora to be a decent bullet-hell type game but nothing too special.