4. Solo Campaigns
The majority of Resident Evil 4 was a solo fare, right up until you had to escort Ashley for a section or two- but it was Resident Evil 5 that had the player lumbered with a God awful AI partner, thus kick starting the trend of making Resident Evil a nightmare- for all the wrong reasons. Part of the fear of the original was going at it alone with no backup, giving a sense of hopelessness and isolation. All to often in Resident Evil 6 you ended up struggling against a horde of enemies- only for you to be bailed out by your partner. Very anti-climatic to say the least.