I, personally, have several genres that interest me, but really only one that will draw me at all times. That being said, however, the genre isn't always enough to get my attention. This is for several reasons, all of which I'm completely unashamed to admit::
My biggest pet peeve- The site has to be aesthetically pleasing.
I know this is something not everyone agrees with, but I'm a huge sucker for a well put together site. This includes graphics, the way the site is built, the colors, the fonts. Do I have trouble finding things? Do I understand what the roleplay is about from the header alone? Are the forums upside down...by that I mean is all the information at the bottom and the RP at the top? Can I read everything easily, or am I having to guess what it says in the forum headers?
One other part is "Do they allow creativity when it comes to posting templates? This one isn't always a make or break part of a site for me, but it is something I always look at. While I understand wanting your site to look uniform, I like my creative freedom. I like coding my own boxes, showing them off, having fun with them and personalizing them to my characters. Being forced to use one identical box that is exactly like everyone elses is frustrating to me, though not something that will cause me to say no to a site if everything else is going for it.
I hate to admit it, but the aesthetics of the site usually come before the plot, which is kind of sad, I guess.
What about you? Are aesthetics important to you? What about the ability to use your own templates? Do you prefer the site to set them up for you, or would you rather use your own creations, or ask someone to make them for you personalized to your character?