It's a great way to get from point A to point B, it's a great workout if you're "maybe you should have a television show" levels of obese, but if you're reasonably fit and not completely sedentary in your day-to-day life it is pointless as a means of exercise.
Context matters and in terms of good means of exercise it does not take much for walking to fall pretty far down the list.
I think "pointless as a means of exercise" perhaps overstates it a bit. I agree you're not going to see much benefits in terms of cardiovascular fitness, but every bit of activity figures into one's energy balance. You often hear that even small little movements throughout the day (non exercise activity thermogenesis) can be the difference between maintaining weight homeostasis or having a few pounds a year creep into your life. Prioritizing walking seems like a good hedge against this if you're not blessed with NEAT.
I know lots of people who are anywhere between bemused and actively hostile to the idea that walking might be a worthwhile activity, either on its own or as a transportation mode (and this in a region with decent pedestrian infrastructure, and temperate weather).
