Plugins allow endless possibilities. Whatever you are looking for probably exists already. Facebook/twitter/whatever integration, fancy widgets, syntax highlighting for code, caching, Google site map generators, you name it.
Install plugins without leaving your WP admin page. No geek skills required.
Comes with an automated backup plugin. Backup your database and email it to yourself daily. Do this!
Upgrade your WP installation with 2 clicks. Maybe 3 (didn’t actually count, but it’s just clicking).
The layout is super-flexible. 1, 2, 3 columns? None? Make your site look like less like a blog and very CMS-like? No problem. There are themes for all that.
PHP & MySQL hosts are everywhere. You’ll have no trouble finding a host at all. If you don’t want to do your own hosting, you can always create your blog at wordpress.com.
It’s Open Source and has a huge community. This means that WordPress will never die! *stabs and Amen break start here*