Unreal engines 1, 2 and 3: Most successful engine family ever?

id Tech 3: The ability to customize the visuals and other aspects of the games using this engine. Is exactly why people love games using this engine. This is highly important for competitive gamers, they play with pretty much no visuals on at all. Unless it improves the ability to kill, something that helps with the ability to recognize the opponent faster and so on. It is all about the need to get consistent over 70 frames per second, no matter what happens on the screen. This is why the ability to strip all eye candy is so important.

Call of Duty 4 engine: Doesn't have name as far as I know. The ability to handle huge amount of effects and still keep up at consistent 60 frames per second, is simply stunning IMO.