Shudder is a top down horror shoot 'em up. You are a lone soldier in a hell-like underworld full of ghouls, possessed insane humans and terrifying monsters.
The game is controlled like a 3D first person shooter, using the W, A, S and D keys for movement, and the mouse for aiming. You have primary and secondary weapons, and can rotate through primary choices using the Space Bar. Shudder looks like a game for an 80s computer, so if you're put off by retro, blocky graphics this won't be for you.
There are three chapters to choose from, and two difficulty settings. Neither are easy! The difficulty comes from your character being quite fragile, and having no check points on levels, so every time you die you have to start again. While it is difficult, it's also an effective horror shooter. There are a nice variety of enemies, and some do create a sense of panic! Like Doom, there is a puzzle element, in that you have to find keys and switches to get to the exit of each level, and these often trigger traps full of monsters.
While the graphics are decidedly old school, the sound is what gives Shudder its atmosphere, with great monster effects and eerie sounds. Aiming with the mouse works great, but it's still difficult, and many monsters will require you to retreat to take them out.
Shudder is a surprisingly scary retro style shoot 'em up.