Games that have two types of movement going on at once, such as head bob (as you walk your view slightly bobs up and down) and weapon bob (as you walk your weapon moves up and down) make me sick every single time.
Eric Qualls, via about.com
As well as field of view, other differences between what the eye sees and brain is expecting can also be enough to completely prevent play. The more differences implemented the greater the chance of issues.
Common issues are asynchronous weapon bob/walk bob, motion blur, mouse smoothing, camera shakes or tilting, or changing where the character is looking without the player’s input (e.g. 01:55 in this Star Citizen footage).
These can be highly desirable for aesthetic and immersion reasons, but if including them, provide an option for people to turn them off.