[Ulthar88]

Genre: Fantasy, DF, Science Fiction, Supers, Space Opera and others. Which make you say "I've got to play this", and which do you particularly avoid?

I'm not too concerned with genre... I do tend to prefer fantasy or SF, but that alone doesn't make much difference to me.

Activities Planned: Do you prefer solving puzzles? or is it combat that enthuses you? How important is character development? Is negotiation an enjoyable part of play?

I enjoy all of the above, but considering the strengths & weaknesses of the PbP format, combat should probably be de-emphasized outside of arena-style games. And while I can enjoy character (CP) growth, I do think it's completely unnecessary to a fine game -- I can take it or leave it.

Supplement materials: Which sets of rules make or break a PbP game for you? This includes Cinematic vs Realistic, G:Magic, Thuamology, Supers, Psionic Powers, DF, MH, MA, and so forth.

Not much of an issue for me so long as all of that is stated up front... and supplemental rules do not cover too many books (just for the sake of my sanity).

Plot: how important is the plot? do you avoid games without it, and only go for ideas that sound cool? do you prefer just wandering around letting characters make their own decisions? And is this question even an issue?

While there should be some purpose to an adventure, I become immediately bored if I find that said plot is really a script and there is a predetermined path to the goal. I rather insist on some level of sandboxiness.

Power Level: Do you love working with mounds of points? is such a prospect dull to you? does it matter by genre? similarly, (but not the same) do you enjoy being world shakers, or do you want to deal with peers? or is this even an issue?

I confess that point totals over 400 or statements like "try to keep disads below 125" cause me to veer off sharply. (With the exception of full-on Supers games, of course.)
And probably a corollary to that -- I strongly prefer playing a credible individual, rather than some wish-fulfillment avatar.

House Rules: Are they annoying or wonderful? If depends, what determines this? or are they just all par for the course?

Any should be minimal, stated up front, and very clearly worded. I might make an exception for a well presented original supplemental book (something like "MyPsionics", for instance.)

Gaming Group: Different players and GMs cause games to behave differently. when using PbP on this forum, how important is who is already playing in the game, or GMing it?

The only way I can survive in PbP is to be very flexible and accommodating to other folks' playstyles. Only in the case of someone who genuinely annoys me will this be much of an issue.

Other issues: what other issues strongly effect how well a pbp game runs?

Although I agree with some previous posters on the importance of consistent posting frequency and styles... I have come to believe that this is a virtual, if not literal, impossibility within this universe and among this species.