Unfortunately, Wikia have decided to change the layout of every wiki they host. This is a major change and is going to drastically change the way in which we use and edit the site. If you wish to find out more about the reasoning behind this, take a look at this blog post on Community Central.
These changes will come into effect in about a month. We hope to have redesigned pages around this by then, but there's no guarantee we'll be able to fix everything in that time.
There should be an alternative skin available called "Monobook". It looks a lot like Wikipedia's interface. If you wish to switch to this, go to the "Appearance" section in Special:Preferences and switch the layout from "Wikia" to "Monobook".
Obviously, the CSS has not yet been finalised and some things look derpy, but that's basically what it will look like. Again, to clarify, it is not us making this change, it is Wikia itself. We will have to redesign much of the site's content, but we will provide help on how to get used to editing with the new design. If you have any questions, feel free to ask below.
I have put this in the comments section below, but it appears that the release of this update had been postponed due to the extreme negative reaction on the blog post announcing it. This isn't confirmed, but the fact that we're not yet being forced to use this new layout kinda verifies this.