What is most valuable?
WordPress started in 2003 and for a long time it was viewed as a blogging platform but in the last 4 years it has come on quite a transformational journey. With it's wealth of low cost and well support plugins, it can provide customer solutions to even large scale membership based websites.
WordPress is easy to install and is a really nice CMS . The ability to amend the PHP to add extra functionality of to tweak things is also a great bonus. The use of PHP also helps if you need to buy help in from a coder - PHP is common so there is a massive pool of devs.
It also doesn't need a massive server to run. That's great for smaller businesses who don't want the hassle of large cloud contracts.
How has it helped my organization?
I volunteer with various charities and WordPress is a very popular choice of CMS to allow them to have great functionality and a solid web presence. WordPress has allowed small organisations to control their web presence cheaply (or in most cases, for free). I think opening up the www to businesses, charities and organisations like this is a great thing.
What needs improvement?
Good point: It has hundreds of thousands of plugins.
Bad point: It has hundreds of thousand of plugins.
You pick a plugin, it seems well supported, you spend time installing it and setting it up. With the next WordPress back-end update, the owner of the plugin may not update their code so you are left with something that, at best, works but could be exploitable. So, it's a cloud - but the silver lining is the choice of plugins :D
One of the most major down points: everyone and their dog tries to hack it. If you use WordPress without security plugins then things won't go well for you. Thankfully, as above, there are lots to pick from: TOR blockers, IP blockers, whitelists, blacklists... all free.
What do I think about the scalability of the solution?
This depends where you have it hosted.
Which solution did I use previously and why did I switch?
I've used Joomla and Drupal which isn't so usable for the average Joe.
How was the initial setup?
It's a simple click through process that takes 5 mins. There are loads of guides on line to help you through it if you are unsure.