For me, the cast is a very decisive component. It usually makes or breaks the role-play for me.

If the players (or characters) involved are dull, closed-off, or personally irritating, I won't apply. I don't want to write in an environment where I can't get along with the other writers because, from experience, it tends to create a very bad and sluggish environment. The same is true for characters. If the accepted characters are flat or obviously over-reaching, I'll take a rain check on the game - there's no reason for me to subject myself to half-baked ideas.

Players/Characters aside, I'm also a harsh judge on writing. I prefer my role-plays to have quality writing. I don't necessarily need paragraphs upon paragraphs, but I do want fun and creative posts that offer more than an amalgamation of all the adjectives in the English language. Prose can be nice, on the off-chance, but continuous descriptions about things nobody cares about gets to be rather off-putting and, in a way, very uninviting.

If the creator's writing is lacking (poor grammar and spelling), I'm, usually, sitting on the fence (assuming the rest of the cast is acceptable). Additionally, I think the tone the creator sets for a game is very important. So, people who think swearing in the rules or being a high-and-mighty bitch throughout the introduction makes them "badass" - I would reconsider that opinion. But, that's not to say, tasteful coloring of a role-play is something I'm against. I just think it takes more skill than the typical: Here's my idea and these are my rules, please follow them!

Outside of those things, I'm not too picky about the kind of games I join or take an interest in. But, even if a role-play appeals to me, if I don't have the time to join, I won't. I don't want to leave people sitting around all day, waiting on my sorry ass to post, haha. So, in a way, I suppose one of the biggest concerns is free time and whether or not I have any of it.

(I usually do not - evident in the fact that I still haven't picked up a game yet, lol).