I just finished DMing my third ever session of google+ (or any internet) d&d. I was rolling both encounter checks, and percentile chances that various creatures (people) would be in their lairs, and happened not to get very many encounters. This resulted in a large number of unoccupied rooms. I feel like in a face to face game, although this might be a little slow, you could sort of handle the rhythm of it in such a way that it wouldn't be a problem. But in Google+, somehow it doesn't really work. I noticed it even in my last game, where the players went through (only) four rooms without encounters, before moving into some pretty gonzo high action stuff and already it was like I felt like the thing was dragging before the action kicked in.
Here's a theory. Here are some features of the game I was running, and also those I have played in on G+ (1) They are episodic in nature, in that there is no presumption that the same group will be present each time, even if there is a hoped for continuity. (2) Everything begins and ends outside the dungeon, for the same reason. (3) XP for gold. I like all these features a lot. They're perfect for playing D&D on google+. They also (self-consciously) mirror early D&D practices, e.g. in Gary's Greyhawk Campaign.
I think these features partly explain some of the facts about rhythm. Take the episodic nature of the game. If I play in a session where some goal is worked towards without being achieved, that's disappointing because I might not play in the session where the payoff comes. Another part of it is, I think, the treasure for xp rule, again a classic. Like, if everything is being measured (goal-wise) in terms of the treasure haul, then there's huge pressure to have at least a whiff of a lot of treasure every time. 0 gold in a session = total failure.
The weird thing is early D&D had all of these features,but also had lots of empty rooms and low key time. I think this might explain (in conjunction with the huge groups in early d&d, not so much replicated on G+) the otherwise baffling use of the "caller" who leads the group by saying what everyone does discussed in the DMG. I have trouble imagining that being fun if stuck to closely, but it would help handle the flow of the game, moving it much more quickly over multiple spaces where no action occurs so that more "success" could be had in each session.
However, since I'm not interested in having a caller, I think this really will affect how I design dungeons. I'll aim for almost 0 dead space, and more planned encounters that are automatically triggered by moving into an area. This isn't exactly unfortunate, but it is unexpected. It also makes it hard to imagine designing living breathing dungeons with multiple factions cohabiting. So much for Red Nails.