Like a 2D game, in a good way!
This thing looks amazing, and though it's all in 3D, it controls every bit as sharply and precisely as a 2D game, something I could not say e.g. of R-Type Delta.
The game kicks my ass over and over again, but when I die, it's my own fault. There's never a time when I think "unfair, that shot should not have hit." The difficulty is such that after a few hours of play I can barely get through second level on Normal.
One thing you might fail to notice at first is that you can re-collect some of your options (the yellow glowy balls) after a death. They float around for a little while. This is a huge deal because without the firepower you'd be screwed after first death.