Every RE game gets boring after about 3 playthroughs so to make it more fun I always add restrictions to my playthroughs.

RE1: Can't pick up any weapons. must playthrough with what you got. (with chris this is hell because he only has a knife)
RE2: Can't carry ammo and can only reload your gun at item boxes
RE4: Can't buy guns from the merchant, you can only use "free" guns (Handgun you start with, Shotgun in house, punisher for 10 medals, broken butterfly in castle) you can upgrade the weapons but you cant buy them.

what do you do to make the games more interesting?