I feel great for it, and I'm definitely way healthier than I was when I was younger.
That said, I've found walking hasn't been enough to keep me in shape alone.
It does little to nothing for my flexibility, and whilst it's great for my legs (and possibly core) it does little for strength elsewhere. I also struggle if I need to really get my heart rate up.
1) Walk everyday.
2) Vary the pace i.e. brisk walking interspersed with slow walking.
3) Use weight vests/weighed backpacks/ankle weights from time to time.
4) Do uphill/downhill and/or up-the-stairs/down-the-stairs periodically.
5) Walk after Meals and after Exercise.
6) Get up and Walk during breaks in between tasks.
Personally I found this with running. It never became a consistent habit and something I looked forward to until I stopped thinking about where, when and how fast I was running and just did whatever I felt like. This realisation came after many years of trying and failing to stick to any kind of cardio exercise, and now a couple of years later I have a few half marathons under my belt and am training for my first marathon later this year. I attribute this entirely to the mindset change I described.
Walking in nature (aka trees around) has proven health benefits also.