I love horror games, but they have to be played in the dark with a good sound system, pref. headphones for full effect. Played like this, although RE4 was definitely more action than horror, there were a few creepy moments in that game: The first "running" through the water in the Novistador section after Ashley's re-capture #1. Ditto the tension just before Verdugo. The Regenerators with their raspy death-rattles were pretty creepy and the "burning man" jump scare was not bad. The death and decay throughout the first section and the night storm scenes were atmospheric, but not really scary. There was not much set-up for real scares, unlike:

System Shock 2, which is is a great horror game. In fact, I enjoyed more than any other game I've played, including the 2 Half-Lifes and RE4. The soundtrack (esp. mutants and "nannies") raised literal goosebumps and the first few ghost sequences were very creepy. The rapid shiffles of the "assassins" were good for a scare, too. In fact I'd call it the scariest game ever. I'd love to see a decent re-make or spin-off of it.

Judging just on scariness, not overall game quality, my top-5 list would look like:

System Shock 2

REmake

Silent Hill 2

Alien vs Predator 2 (Play as Marine)

Call of Cthulhu: Dark Corners of the Earth

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Honourable Mentions:

Eternal Darkness

Sanitarium

Half-Life 2 (Zombie Town Chapter)

Undying