There are many features I love about vim, and most are the usual ones (not so many key strokes, no need to move the hands to the arrow keys, no mouse required, syntax hilighting for 300+ file types).

But one is really that it makes reading text and editing text different things. That's very helpful when you read source code, and you have a barrier before changing it. That barrier is quite low because many different keys place you into insert or replace mode, but it's there, and I like it.