Here's my perspective as a player and a signer-up, in sequential order:
1) Originality. I will read literally anything that isn't the same five genres we see on the Guild every damn day, even if I feel assured that I won't like it. This isn't necessary for the game to be good but it's the first opportunity any writer has to hook people. And of course, if your game is more derivative then you're competing with the other hacks in your genre, some of whom may have done said genre more favors than you. So ... be original. Own a monopoly over something. I promise at least one person on this shitty site is gonna read it, possibly even give it a shot.
Originality can be something as simple as a badass title which sounds intriguing without telling me exactly what the RP is about. I'm not going to click on the fifty-third "Welcome to [So-and-So] Academy" or "The Knights of [Place]" this week, but I might just click on (credit to
@The Harbinger of Ferocity)
The Twenty-Fifth Hour. I have no fucking clue what this RP is about just from reading the title and that's a
good thing. I have to click it to find out and a click can easily become another player signing up purely if the hook is novel enough.
2) Quality of prose. Once I've clicked the thread I'm checking that the GM knows the rules of style and has worked to develop a style of his own. It makes the mandatory reading of his thread far more interesting if I would also be happy reading it on my own time; and he will probably tend toward choosing better player apps for the game as well.
3) If the game has passed #2's criterion then I head over to the Char tab, or the posts responding to the IntChk, to see who else the game has attracted. It's unfortunately all too easy for the players to bury a talented GM; they may be misunderstanding the themes, motifs, & imagery he wants for the story; they may be getting out of control with technology, magic, or other character powers; they may simply be introducing an aesthetic to the RP which will stand out against the GM's. No fault of his own, but there are certain kinds of players who I'd simply rather not fuck with IG, either because I know them to cause problems and drama or because their ideas clash too hard with the GM's vision. I know that's an inherent fact of RP ... that it's not just one person's vision, and you need to be able to collaborate with others to make it work ... but I've been RPing long enough and made these mistakes myself enough times to know when a sheet is a dealbreaker for me and when not.
4) So the GM and characters both seem promising. The next question is: how much effort will I have to put forth in order to join? Sounds lazy, I know, but there are two facets to this. One is knowing I can handle the responsibilities of the RP and keep up with its expectations, in other words, that I won't fuck over the GM. Two is that the GM expects reasonable things from me. If he's very rigid on how many times I have to post per week, and that number is higher than, say, two, well, this is a GM who doesn't understand that RP is a hobby and not a salaried full-time job. Moreover I don't want to fill out a character sheet with requisite details which fundamentally damage a story when they are known upfront; for example personality sections, like/dislike lists, and relationship sheets, the contents of which firmly belong in IC; you showing-not-telling, your partners inferring from and reacting to the subtexts of your posts.
There may be more that I have not thought to reflect on, but between these three big points (and one minor point) I'll already tend to have a good understanding of how compatible I am with the GM, how long his game will last, and whether I am capable of upholding all expected obligations for the entirety of that duration.
Thanks for coming to my TED talk.
P.S.
@BrokenPromise is right. I'd say "cravings" are cancer except cancer lasts more than two weeks.