I can't compare it to Krabi town because I haven't been there. However, Ao Nang beach is a great little place. It all runs along one long road that first leads to the beach, then turns right and runs parallel to it. There are plenty of tuk tuk drivers around, so if you're feeling lazy you can grab one of those for between 20-40B depending on the distance.
I like the walk and from just about anywhere further away it will take between 10-15 mins to walk to the corner of the beach to get a long tail taxi boat.
We stayed at the top, as you come into the area at a hotel named Haleeva. The room was nice and the staff incredibly helpful. In fact, we booked our bus to Bangkok through the hotel. It cost 600B. I will tell you about that after the journey.
There are plenty of little shops to peruse. There is a Subway, Starbucks and a McDonalds for those looking for normality. This would be a mistake, Thai food is delicious everywhere!
I ate a soft shell crab curry last night at a place a stone throw away from my hotel. It was certainly tasty.
Here are two pictures: one of the beach and the other was the view from our hotel window.
Be warned, if you are a light sleeper don't stay near one of the two mosques. There are multiple calls to prayer and if you are close enough you will hear the whole prayer time. I personally think this is awesome and don't have a problem hearing this. The earliest is around 5am.