I think for me, the thing that gets me most hyped regardless of genre or subject, is quality roleplayers or roleplayers whose writing styles I personally enjoy.

The backstory and lore is always what gets my attention. I could hardly care about the writing style - I've seen good and bad roleplaying styles, but regardless everyone wants to have fun.

interacting with people I know, even if it's not very well.

Interesting concepts, both in the RP and characters presented.

Being the GM helps, but is not required. Haha!

• ① Premise. If the GM isn't doing something outlandish and clever with the setting, plot, and genre, then at the very least he handles them with reverence, and attempts to craft an RP which delivers all these things competently. It's OK to be derivative sometimes but then the RP needs to deliver the feels associated with those respective genres; people don't join Post-Apocalypses for the comedic relief.
• ② Depth. The world the GM delivers to us is not simply a gathering of characters; it is a place. Every DMPC/NPC has his own motivations, fears, and flaws, just like a good player-character. The PCs meanwhile are given special treatment for earning and deserving it IC, not just for being PCs. Furthermore, characters are not put on a tour bus and driven from one location to the next simply to admire the architecture; these locations all feel like they live and breathe with the same spirit as the people who inhabit them.
• ③ Literary realism. Dragons and magic and floating islands don't excuse characters who smirk all the time to prove how badass they are. People act like people, not like deranged power fantasies, and the GM enforces this philosophy both in the players' writing and in his own.
• ④ The other players. No matter how good a premise is for a thread, I always read the character roster before choosing to join, because Mary Sues, edgelords, and really, any players who don't understand the importance of tone and atmosphere to a group of characters, can ruin an RP as ruthlessly as can an incompetent GM himself. For example, the reasons for LotGH's supremacy over Code Geass are many, but chief among them is that one is a serious military drama about adult men with realistic visual designs, while the other is a "serious military drama" about high school-aged children with green hair and purple eyes. Tone cannot be ignored in writing an RP which strives to be great.
• ⑤ Conflict. No good RP has ever arisen from an echo-chamber. A smart GM allows OOC debates to occur in order to test the strengths and merits of his players' ideas, and the players embrace IC conflict in order to test, harden, and develop their characters. The cowards who beg for the fighting to stop inevitably castrate an RP and consign it to mediocrity.
• ⑥ Strictness. A good GM cares about the sanctity of his world, and he is not afraid to refuse access to people whose ideas will dilute or damage his own, nor to punish those who damage it from within. Perhaps he will compromise with them, and help them to come up with better ideas which are apter for his thread; but regardless of method, he will have the spine to enforce rules, regulations, and standards over it. (There is no such thing as a good Multiverse RP.)
• ⑦ Intellectual equality. The GM doesn't "railroad," so the players are free to manipulate the world as they please. In turn the world (the GM) reacts to their actions in realistic ways, punishing their mistakes and rewarding their success. The characters are able to change this world, for better or worse, and the GM trusts his players to treat his world with respect. Ergo, the relationship between GM and players is not that of a shepherd guiding a flock along a perilous mountain pass; it is a symbiosis, like the algae and the fungi which together form a single colony of lichen. One cannot survive without the other, and in the RP everyone's ideas are weighed by merit, not by their "rank" in the colony.
• ⑧ Titties and ass.

Securing the RP's future is equally important for its success as is laying a strong and sturdy foundation upon its conception. If a thread boasts most or all these attributes, I am very likely to make room in my schedule so I can participate in it.

TL;DR If you think snarky tumblr gifs, cute CS formatting, and knowledge of the difference between their and they're are the only things you need to make fantastic RP, you're kinda wrong.

If I know or see someone to be a really good GM, I feel confident in the depth of the material for the story, and their ability to filter out characters that might make the story less realistic (e.g. overpowered characters). When other participants show some care in trying to understand the world the GM has created, and are respective of other characters, that's quite exciting as well. That's how I generally judge whether an RP will be exciting and successful - at least for me personally.

I'm speaking solely from a 1x1/possibly small group perspective, since I tend to find little luck in larger group RPs nowadays.

For me, setting a good relationship with my future partner, and for the pair or group of us to be able to talk out and plot a good "forward direction" for the setting or plot, doesn't necessarily have to be in depth but certainly should allow us to decide together what kind of tone etc we want for our plot, whether we want to go gritty and dark or happy and cheerful or a mixture of both and so on.

Also good effort on the other persons part to help me keep the plot running. Nothing irks me or kills my enthusiasm for an RP more than a person who ignores what we previously discussed about a certain plot (particularly in fandom cases) to then post nothing but half-liners or one liners (I have no issue with short posts, don't get me wrong, AS LONG AS they give me something to respond to) that are internal brooding/monologuing that my character(s) can't even respond to.

Actually doing it and having fun with it. :D

Don't care how detailed, how smart you are, how interesting the theme is. Are you active and are you trying to RP like it's suppose to be fun and not a unpaid job? If so, then you're already doing more right than most people...

Maybe it's because I've had some bad luck with RP's in general. But nothing is better than actually getting to have fun, and actually be role playing at a consistent pace.

We agree with many of the sentiments above. Thus we won't reiterate them in any detail. (sentiments like the ones in @pugbutter's post)

What we also consider important, especially so as GM, is players who hold some or all of the following traits and behaviors:

• Get involved. Not only do they set up plots of their own, but they partake in the plots made by the GM(s) and the other players alike. Their characters are connected to those of other players and are affected by them in positive and negative ways. Loner characters are easily crafted. _{(we've made too any of those...)} Whereas characters connected to others requires more work and depth of design.
• Listen. Good GMs have a plan. If a character concept does not fit with that and the GM(s) say so, we respect players that listen and do not keep trying to push the same dysfunctional concept over and over. We don't kick players for making a bad first sheet. Either not understanding the criticism (and not asking questions) or trying to barge on with the idea in spite of the criticism, that annoys us. _{(Yes, we're looking at those who seek Mandalorian bounty hunter Sith Lords in star wars settings)}
• Stick around. RL can throw a wrench into any well-laid plan. Inspiration can suddenly falter. We respect players that stick around even if life is bad. They don't have to participate much (or at all, really) if life is truly bad, but we hope they take the time to give word. It doesn't have to have any detailed explanation. A simple "Gone for now. Dealing with RL." is satisfactory in our opinion. Sure, everyone likes knowing more, but that doesn't mean the other party wants to share. We'd rather give a player a week or three off than lose him (or her) permanently.
• Communicate. Sometimes, a player ends up dropping an RP. While we as GMs appreciate knowing why, we won't demand a reason. What we detest however, is the kind of player that drops an RP without telling the GM(s) they're dropping. Most frustrating of all is when a player simply disappears, then keeps on being active in other guild RPs, and when contacted by PM about whether they're still in the RP, don't bother to reply.

@Ellri I wish that simple loyalty and devotion to an RP weren't such rare traits that we have to talk about them like they're special qualities. Nice post.

Eh, probably a multiversal crossover RP.