Resident Evil: 10 Reasons It's The Best Horror Franchise Of All Time
6. Link Between Puzzles & Exploration
You start in an enclosed area and have access to only a few parts of it. There are monsters, and a few strange items that catch your eye. Finding time away from the monsters you'll be able to figure out that this can be used here to get that which can be used there which unlocks...
That's how Resident Evil puzzles are built into the exploration of the world, leading you to unlock more and more of the environment as you explore and try different things out.
You'll find yourself going back and forth between new areas and old places that need an item for you to continue, opening up even more of the game, and exposing yourself to the monsters even more.
Some of these things you unlock will lead forward through the game. Others will lead to more supplies that you'll need for later, or more powerful weapons. The majority of the games are brilliantly balanced between these two sorts, so that replays offer a lot of optional content that can be avoided if the player has the guts to barebones it.