Doom's first half hour is explosive. You wake up and punch everything in your way before acquiring a suitable weapon to waste the screaming demons running for your face.
After a quick sojourn through some corridors and up an elevator, the game opens up massively. The title screen drops, metal music blares, you're outside, on Mars, and demons are everywhere. Welcome to hell.
It's exhilarating and fast-paced; damaging enough enemies allows a window for a melee "glory kill". The enemy will flash and after any number of graphic deaths, you're rewarded with ammo and/or health.
As you progress, more enemy and weapon types appear. Some are nostalgically familiar while other grotesque imaginings are new and exciting.