I would suspect that a playable and fair course means different things to different people, but in general, if you can play a course and score close to your normal handicap / score, then the course is probably considered fair and playable by most golfers. I suppose that the same course might be fair for a better player but unfair for most high handicappers, or vice versa.
Lots of water or OB, at least for my game, can make a course seemingly unfair. A few water hazards here and there are OK, but if I am losing major stokes every two or three holes to the water, then, at least for my game (scores int hehigh 80's / low 90's), the course is unfair. Maybe for a better golfer the same is not true.
Many newer courses have to much water...it is the one hazard (along I guess with OB) from which there is no recovery, whereas with sand or trees there is usually a chance for a save.