A good Players Wanted ad needs to be brief. Who is going to be so interested in it that they'll read a Great Wall of text? Precious few potential players. But it needs to be informative. It needs to convey in brief yet clear tones what kind of game you're looking to run, so that the bites you do get will be the right kind; there's no point talking to lots of potential players to find out that all they really want to play is an elf bladesinger in a Forgotten Realms campaign. You want it to be specific enough to act as a self-selecting filter for the kinds of players who you are likely to mesh with, but you have to be careful with that so you don't come across as a holier-than-though stick-in-the-mud elitist with finicky tastes, which would be off-putting to exactly the same players that you're hoping to attract.
And most of all, it needs to be evocative. If in your pursuit of brevity and information-sharing, and correct tone placement you manage to come across as dry and boring, then you're not likely to get any hits that way either.
One good way to do so is to use the "Hollywood style" pitch idea. This is a very concise comparison of your game to a few other well-known titles, characters, or elements in the hopes of drawing attention to the similarities between them. Famously, Star Trek, the original series, was pitched to studio executives as "like Wagon Train to the stars." You probably want to be a little more exacting than that, but not much longer. And some kind of snappy graphic--a banner ad, or a fantasy picture that is evocative of your setting, can't hurt to help grab attention.
So, here's my ad--sorta. Normally, I'd actually put this in Word, pdf it, and print it, but for now, I'm just doing it as web text with a banner. It might not be perfect, but it should at least be a good enough example of what you're looking to do.
A homebrew setting and game that encourages wild swashbuckling action, gritty noir investigation, and Lovecraftian dark fantasy in equal measures.