It's MediaWiki skin (theme) "oasis" is horrible and the customer service is not very good. It also is a pain to move from Wikia when you want to host a wiki yourself. Why? Because when you ask for your Wikia to be deleted, they blatantly deny the request. If you move from Wikia, getting the other users to move to the new wiki is extremely hard.
Just learn how to make your own Wiki using the open-source PHP application: MediaWiki. If you are unable to manually create a wiki, use ShoutWiki. It's a better wikifarm than Wikia is.
Also, some of the content isn't for kids.
It's really hard to visit Wikia because of the overload of ads, which makes pages load almost infinitely. As well as that, there's a lot of issues with privacy and cookies. Content on some wikis could be considered not suitable for children, spam and hateful. Overall, if you need to host a wiki, don't do it at Wikia.
Wikia have stolen my site from me. I have attempted to move my wiki to it's own host, and Wikia are refusing me the right to delete the old one, or even to link to the new one from the old one. They are doing this only to collect ad-revenue. Wikia are a greedy, power hungry website that should not be trusted.
Some people swear too much, and that mostly goes for bad moderators. A perfect example of this is shown on TheRobertsFamily3's page on Toontown Fanon Wiki. (if it still exists) "F*** YOUR S**T WIKI! I CAME TO RUIN YOUR LIFE, A**HOLE!" That kind of stuff may appear.
And there is sometimes a-lot of spam too. And bad and/or unrelavant pages.
Also, when the moderators accidentally block you forever instead of blocking the real criminal, they DO NOT let you communicate with them. If you get IP blocked forever, time to start using Wikia on a new computer - and under a new identity.
Other than that, it's still pretty good for all of this spam, hate, and even lack of communication.
Once started on Wikia always on Wikia. There is no way to stop a Wikia site. I still see people falsely going to Wikia services that are officially down and moved to another location (WoWWiki that is now Wowpedia is the perfect example fo that, and much more are there I'm sure).
On top of that the adds are very oppresively there and in a more prominent position that the information you're trying to look up. More and more Wikia is turing into an advertisement only site and not into a host to host a wiki on.
I'm quite sure that I'll never start my wiki here if I ever consider to make one!
Wikia's customer experience is bad in many ways like:
1.Forcing users to use the new Wikia skin
2.No staff listens to your suggestions
3.Lots of ads
4.Merging and forcing existing wikis to use Wikia
Because of this, Everyone is moving to another wiki farm.
This site makes some very weasel-worded and misleading claims, like "we will host your content and the wiki is owned by the community". The truth, however, is that Wikia could not care less what "the community wants". They've forced two ad-heavy reskins on users (in 2008 and 2010) and censored content to dumb wikis down to a PG-13 level. When the authors of these wikis have left in disgust to build their own sites with the free MediaWiki software installed on their own servers, Wikia has left the old, abandoned copy of the project open on the old URL as a direct competitor to the new wiki. This has done immeasurable damage to online communities as it appears to search engines as duplicate content, which is penalised heavily. The one exception? Apparently a Spanking Art Wiki was able to leave without Wikia using their content to operate in direct competition with their site on a new host... but then only because an outside "Wikipedia Review" site threatened to say some very bad things to Wikia's advertisers.
Wikia has ridden on the coattails of Wikipedia for far too long; the latter organisation is reputable, but Wikia is *not* Wikipedia despite using free software developed for WIkipedia. Don't be fooled. If you want to start a wiki, register your own domain name, download MediaWiki and install it on your own servers. Stay far away from WIkia or others like it; once your content is hosted on their domain, they 'own' your inbound links and search ranking while they slowly destroy your site and community with endlessly-increasing amounts of spammy advertising.