Wordpress can be used for wide variety of websites and it is the most widely used CMS. There are plenty of plugins, that greatly extend its functionality. There are plenty of Wordpress themes both free and commercial. Wordpress was originally designed as blogging tool. Since Version 3, it looks more and more like complete CMS. Wordpress websites are easier to administer than websites build with Joomla and Drupal. That is usually one of the factors, when I am building the website for a client and decide on the software for the project. So, how easy is to administer Wordpress website? That would depend on the type of the website and the skill level of the administrator. Another important question is who and how would be updating the website. Performing updates on the website does require proper skills.
Best case to use Wordpress:
It would be a good choice for blogs and small websites. It also can be used for e-commerce websites. Another option would be to use Wordpress as platform for further development, but that would be a better choice for larger companies with their own development teams. Just because you can build more complex sites with Wordpress it does not mean that it is the best tool for the job.
Wordpress is very limited at what it can do out-of-the-box. Yes there are thousands of plugins, that greatly extend its functionality, but you should consider how many plugins you would have to install and how they all would work together. Many plugins and themes come in both free and paid versions. You often would need to buy paid plugins, because free ones have limited features. Another problem for both free and even paid Wordpress plugins, that you cannot be sure that plugin would be supported and updated by its author and it could cause serious problems, if you have a lot of content, that depends on that plugin. About the same can be said about the themes. Theme's features are important for many Wordpress websites and you often would need to buy paid version of the theme. If you change the theme or even if the theme get updated, you may need to edit some custom code for your website. Updates can cause problems with themes and plugins.
Other option would be to write you own code. If you decide to write your own code you would need to consider future updates and maintenance, as some code would need to be regularly updated. And if you have to write a lot of code, what is the point of using CMS? Another issue, that is unfortunately also common is the quality of the themes and plugins. Yes there are some guidelines for the developers, but there is no quality control from Wordpress. So almost anyone with very limited skills can develop themes and plugins.
You should also consider how many plugins you would need to install on your website. Plugins do slow down Wordpress websites. They also may cause conflicts with other plugins. Some themes also can affect plugins, so you would need to make sure that plugins work well together and that plugins work well with chosen theme. Unfortunately next update to theme or plugins or to Wordpress core can create problems. Yet another issue with Wordpress, that plugins very often do not uninstall cleanly. That means that you would need to use another plugin to uninstall, what have left after some plugins were uninstalled or you would need to clean database manually. So overall, if you need to use a lot of plugins to build website, Wordpress may not be the best choice and other CMS like Drupal, should be strongly considered.
Another issue with Wordpress is that many of the plugins and themes need to be updated very often and many of them go through endless cycle of updates, bugs and bug fixes. Considering the fact, that you should not update live website, until you properly test the update and you often would need to test few updates at the same time, it becomes major time and resource drain. That would certainly increase time and efforts to maintain the websites and if you are dealing with client you would charge your client for that or do all that work for free and neither of these two option is a good proposition.
Since I am Wordpress developer and Drupal developer, I often compare them for different projects. As I previously said, Wordpress is very good choice for DIY projects, for blogs and smaller websites and also for smaller e-commerce websites. It should work well for different types of websites, if you do not use too many plugins. For large and complex websites and websites with very high traffic something like Drupal should be strongly considered. For larger e-commerce websites, more specialized software like Magento often would be a better choice.
Wordpress also has very good forum support, so if you would need to get help there is very good chance, that you can find the answers or have your questions answered. All-in-all I can recommend Wordpress for variety of DIY websites and, if in the future you would need to add some features to your website, there are plenty of developers, that you can hire.