Been working with it for the past 15 years, and made a good business on it. It's relatively easy to create a hardened install that will -most likely- not get hacked. Slap a caching solution on it and performance is not a problem.
Name me an alternative CMS frontend that any client can use to update/create content (without learning Markdown) and visually design a page with pre-defined blocks, that doesn't cost $200+ a month.
If only they would include a localisation solution, I could say goodbye to slow and cumbersome WPML.