My underlying point is the total package - abilities, headaches, support, and ease of development/fixing makes WordPress very appealing
Again it depends on many factors, and again is not easy to talk about it without comparison, and worse when some of us have developed our own CMS. Anyway, things I've seen, suffered and enjoyed:
WP for you? (us?)or for the clients? that's an important point. With WP there is usually no need for training on how to update the site(or very little)
We can build up a site and due to the massive use of WP, there is little need to train the people who will update it. There are manuals and tutorials on the web already available. If we use our own CMS then comes the need to train the people in charge. No copyright problems WITH THE CMS
Not talking about the thems. You can set up and give away any WP install so your client can have it ready (this applies to any massive CMS). If you use your own you have to give a manual and the rights to use your CMS, perhaps with a fee. Easy to trade
Selling a site is easier with WP (and somehow buying it too) as many buyers ask for a CMS that they already know to just buy and work on it, instead of learning how to work it out, very little to discuss there. Website buyers sometimes ask specifically for WP sites so they can integrate it to their network or perhaps their "one and only WP setup" (old MU style).
The multilanguage thing is very cool, you can sell your site to someone in another country and give your WP already translated, something hard to do with your own CMS unless you implemented that feature, sure other CMS also have this feature. Things to fix
Usually (don't take it personally, is dumb to do it so), "usually" sites built with WP only mean the developer has very little experience on developing scripts. There are experts, yes, but the web is filled with patches sites built on WP. Don't get mad, you WP lovers know the downs of your tool too. No guarantees
Being developed by somebody else (specially the plugins) and having changes that makes some things incompatible, you have no way to ensure that any upgrade will keep your site up or break it down. Drupal per example allows you to have the CORE separated allowing you to upgrade it anytime (except with huge changes in versions). Security
Way better now, but you have to be vigilant in case a bug is found and your site is compromised. I find hosted WP solutions to be better as they take care of this part. Code and HTML
Sure, experienced users would complain about the size and speed, and will have to optimize the WP and the theme. Yes, WP has benefits (as ping) but that's something we can add to ourr CMS if is not already there. Back to the point, some don't like the amount of html WP brings to the browser and there is a lot that we can improve there.
Anyway, that's understandable, it's an out of the box CMS that, as any out of the box system will need and allow you to customize it. Is up to the user/developer
Having lots of plugins to choose from doesn't mean each plugin is worth of trust or that the code is optimized for the job, we will have to double check it for our own sake. Mainstream? fame?
Don't know if that's the perfect expression but WP can be a plus when selling and idea to a client, some associate WP to success just because... it could be a marketing benefit. To be fair I have to bring up the complains posted on this form as when a client needed a project and wanted WP instead of another better solution and then the client and the developer are complaining... Is not the tool the magic one, you have to choose the one right for you. [webmasterworld.com
...] Insisting on using WP or anything, like a hammer to do everything and everything is a fail from the start.
I learned here that we should be versatil and able to work diff tools.
Talking about WP is easy, don't like it? take it or leave it, its our own personal experience. Comparing it? not fair for WP or for other CMS as the profile of the users/developers is very different, take Drupal vs WP users as an example. Worse if we compare WP to our own CMS. The big difference is we can build a CMS for us and can be fast and easy "My CMS weights only 50K" (something I've said too) but others will have problems using it (regular users) things change when you develop a CMS for regular use, easy setup and to just give away... it changes almost everything and begins to grow.
I go with my own for personal projects, then Drupal and then WP but depending the need I can go straight to WP.