I use WP for almost all the sites I manage these days. From my perspective:
- Thousands of free and low-cost themes available
- Database driven, making it easy to switch to a new theme (keeping your site appearance up to date) without having to recode all your content
- Thousands of free and low-cost plugins to extend functionality
- Open source, so easy to modify or write your own theme or plugin if you can't find exactly what you need
- Extremely popular, so there are lots of experienced consultants, designers and developers to help if you can't write or modify something yourself
- The price is certainly attractive
On the downside, since it is free, open-source software, there's no company support line you can call if you have trouble. But so far I've had no problems either getting an answer from the other users on the support forum or in finding a reasonably-priced consultant who could address whatever issue I was having.