Preliminary report: Risus-mediated play-by-post roleplaying is awesome.
Naturally, this is mostly a function of the GMing. She knows her material, and she's taking advantage of the form.
But the form! It exercises some mental muscles roleplaying doesn't normally use. Writer-type muscles.
An interesting challenge: how to get across what my character is thinking without using any internal monologue?
It's also interesting, being able ask the GM questions in the middle of a game. I tend to try to discourage side-talk in tabletop play; time spent one-on-one seriously subtracts from everyone else's play time. I can do that kind of thing out of game, but that discussion takes place on a strategic level.
In this game, if I come up with a question that I think my character would know the answer to, I can fire off a quick note the the GM and the other players are none the wiser. And it works the other way. I can come up with information about my character as the GM needs it.
Which is how I like to work: incrementally. Come up with an idea and spin off of that.
This is a style that fits with me. Writing, collaboration, time to think. It'll never replace tabletop, but if it stays this good I may have to make it a regular part of my gaming diet.
On the other hand, the waiting is going to drive me insane.