Brisk walking can be very good, particularly if you do it regularly.
But beyond being better than nothing, I think it's mostly a great addition to a program that already includes the right measures for nutrition, and includes a strenght/resistance training regimen.
That way you keep your metabolism up, and by strategically creating calorie deficits, you basically make sure that any activity you add to that adds to that calorie deficit (and thus to your fat loss).
And last but not least:
Walking has sort of a meditative effect on me, it's really relaxing