Gaming is an ongoing thing.
I run four online games at the moment, all using the 4e rules for D&D. All four campaigns have been running well over a year. I play in a few games myself, usually between 3-5, so you could say I'm slightly addicted.
All of these are PbP (Play by Post) and my games are run on the Paizo forums - which is slightly surprising, given that Paizo is the home of Pathfinder and Pathfinder and 4e are not particularly compatible. Both systems tend to have rabid adherents who are reluctant to find any good in the other system. Having said that, most of the players I know are more pragmatic than that. If they find a game they enjoy, they'll play it and hang the system.
PbP is a special animal. The timescale is very different to a tabletop game and that has some interesting effects. One of the biggest is that in general the standard of roleplay is much, much higher. It requires some suspension of belief to accept that the very large bloke with a beard is a tiny halfling druid if you can see him sitting right there. If, on the other hand, all you can see is an appropriate avatar and the written word, the character is instantly much more believeable.
Tied into this is that the responses need not be immediate. There is time to think about what a character would say. In a table game, chances are that in any party of more than five, half of them will be wondering if the kettle has boiled yet and the other half will be scouring their character sheets working out how they can fit in an extra attack with bonus damage. Few of them will be paying much attention to the lovingly crafted characterisations of their fellows.
The response time is good for a GM as well. You have time to sort out rules quibbles behind the scenes. You have time to check any more bizarre powers players or monsters use. You have time, in short, to make informed decisions. Those hair-pulling moments of "Ark - how does that work???" can all happen offstage.
There is a downside to all this joy, of course. The timescale issue works both ways. I am in the UK. I have players who are in Australia and various parts of the US as well as a couple in the UK. Different time zones in other words. In a nutshell, this means that any kind of combat or social interaction can be paralysingly slow. It can easily take a week to get through an entire round of a fight and much longer to decide on a plan of action. Some players only really post during combat rounds, others will happily chat for days to the NPCs. A balance must be found.
My own take on this is to be brutal. During combat, I give any player 24 hours to post an action and if they don't I'll either delay them or post on their behalf. Planning and social stuff I am more lenient, but in a PbP it behoves the GM to be pushy. Very pushy. Force them to make a choice. You have to. If you don't you're left with a bunch of characters stranded in the middle of nowhere unable to choose the left or right hand path. This is how PbP games die.