I've played in a couple of play-by-post games over the last couple of years, and they've all ended more-or-less unsatisfactorily. Usually posting would slowly wind down until we hit a bottleneck of some kind and it stopped entirely. Have you ever run or played in a PBP or PBEM of this kind that survived more than a couple of months? Is there anything you can do to make a game like this more successful, in the area of system, style, social contract, or otherwise?
Oddysey. I've run several successful PBPs and several unsuccessful ones. (It's been a very long time since I did PBEM.) These are based on my own experiences only. My advice may be incoherent as I'm going off the cuff and have taken a lot of allergy meds today.
I usually set up a phpBB-based forum solely for use with the PBP, rather than using an area of someone else's forum. It makes it much easier for me to administer and tweak.
I set up custom ranks for each player to indicate which character he or she is playing, which makes it easier for the players and myself to keep things straight. I encourage avatar use as well.
The paramount concern in PBP, in my experience, is having active players. I ask for some kind of substantive post at least once a day. Stagnation is doom in the PBP realm ... once things slow down, heat death follows. If I can't post for a few days - which happens - I let everyone know, and expect the same.
One thing I discovered running a City State of the Invincible Overlord PBP a couple years back is that too many options at the beginning of play can lead to decision paralysis as the players try to decide what to do. In a dungeon-type game, I'd recommended starting at the adventure site, getting stuck in, then getting to the roleplaying after the players have the swing of things. In a story-type game, I'd consider starting in media res, like with a chase scene or something that gets the players thinking in-character quickly.
Another advantage of having your own forum is that you can easily set up "private" forums, each of which only a given player can see. This is useful for "note passing," keeping track of xp and private conversations, and so on without having to go through a backlog of PMs.
I usually have an out-of-character forum for intros, general discussion, and metagame stuff, and an in-character forum for actual play. I devote a separate thread to each "delve," as I'm currently running an OD&D campaign.
Finally, I'd avoid excessive infodump. It's great for you, as the referee, to know lots about your setting, but I'd keep the early background to just enough to give the players a sense of things and parcel the rest out through play.
Hope this helps a bit ... if I can be of any more assistance, especially in the area of setting up a phpBB-based forum, please let me know.
I ran a PBeM game for several years, and have done a number of successful and "failed" with others. I've only done free-form this way, though. (I call it "Collaborative Fiction" when talking to non-nerds.)
One of the keys to keep things going is to be continually recruiting. New blood keeps things alive. For a free-form PBeM, I'd suggest at least 6 players minimum; I prefer 8-10 as my ideal. I've also found some sort of public "standard" helps greatly -- "I will post at least once a week" sort of thing. I've tried "Just post when you're able" games, and they tend to grind to a halt in pretty short order as you've described.
You also want to find and nurture the leader-sorts within the group -- you want people who will kick the group when it slows down too much, either by throwing in new ideas or plot twists or whatever else. You also need to be willing to cut a plot/storyline/quest closed when things start to flag, and start up a fresh new one again -- in my experiences, about a month and a half is enough for a single storyline, which means if you throw in two weeks of down time between plots, you have a nice rough two-month schedule for plots.
The biggest killer I've seen to online play for RPGs is combat with initiative order. So in terms of system, picking one that de-emphasises combat, or at least handles it equally would be necessary. Alternatively, some systems, like Burning Wheel have a combat system that isn't done step by step like most traditional systems, that lends itself better to PBP/E. Another thing is avoiding a system that requires checking against TNs. If you ahve to ask for permission before you declare your action, it really slows things down, but if you can just roll and determine the results yourself, you can string together several actions in a single post. This means d20 systems are a particularly bad fit, because they offend on both counts. Something like Alternity, or even moreso Donjon would work much better.
I have played in and run several PBeM games and as with the other posters, some have failed and some have not. One (sodiumnoir.com) ran for 10 years and it was eventually my failings that killed it in the end. I couldn't handle a disruptive but outwardly helpful player and they eventually ruined it for everyone. Even the person running the game is susceptable to the many things thta can kill a PBeM.
Here are my tips to add the other great advice when running an online game.
1) be strict with troublesome players. The number one killer of an online game is the guy who spoils it for everybody else. You have to keep a harsh control over disruptive influemces, espechially the ones who will spoil the game for you as the GM.
2) share the workload. If the game gets big, give your star players room to run thier own substories. Ask good players to help newbie players, treat it like a community event. If people offer to develope the website, let them.
3) keep everybody reined in to start with. No matter how great a player seems to be, don't let them stretch the rules of the setting or to create an 'unusual' character. make everybody, even your friends you already trust, prove themselevss first. Once they have shown that they are a benefit to this game and this setting, then you can let the good players do kinky things with their characters or even create seciond characters.
4) have a page for the rules of your game. make sure players know the way you deal with non posting and the like. An unyeilding system make sit much easy to deal with issues.
5) make sure players have access to you or the GM/storyteller. Make sure their access to him/her is structured and they don't bug the GM so much he starts to hate the game.
6) the number 2 killer is the GM/storyteller loosing interest. How you prevent this I have no idea. The best games I played in were run in chapters, with natural ends to each story. Even when the GM lost interest and the story fizzled out, they'd still run good stories in the past and that is what I remembered.
7) don't try to fix a lull in the game by throwing new stuff at it. Games can get drown in all the great ideas at times. Every player is a frustrated storyteller of some type and they will all want to throw cool subplots for their character at you. You will want to throw a bunch of cool things at them. Find a way of limiting that and you'll be a better man than I.