Reflex is a sort of shmup/puzzle game that's very simple in conception but rather hard to play.
It's a top-down scroller, with a Brickout-like array of blocks moving toward your ship; you score points for shooting blocks, which disappear when shot -- except for grey "metal" blocks. You need to navigate around them, and suffer damage whenever your ship intercepts a block.
The difficulty arises because of two factors; first, you move with WASD but can shoot in all four directions with the arrow keys. Thus, maximizing your score means alternating shot directions -- and, as in Robotron, dealing with two joystick-analogs takes some getting used to. Also, if you are approaching a metal brick, say, you need to shoot to one side to open up a brick there, slide quickly over, then quickly shoot ahead before you intercept that brick, which is tricky.