LOL...
there is a third variation of the lunge: reverse lunge: where the person steps back and does the lunges then steps forward again completing the rep.
The split squat could perhaps also be considered a lunge.
My experience with lunges per se is pretty minimal since I only started doing them regularly on this program...but I like unilateral leg work in general.
And so far, within the 6 weeks that I have been doing different lunge variations in, I think they really help as supplementary exercises for the deadlift and squat.