Participatory

There are two halves to any experience: the feeling you get when the experience happens to you, and the feeling of being the one who provides that experience. Mostly, we tend to focus on one or the other individually, because you tend to be either the entertainer or the entertained, not both at the same time. However, there are some examples where they overlap, and I think the new kinds of experiences we can craft using computers and the internet make this an area of particular importance.
Most comedy, especially mainstream comedy, tends to be a received experience; you hear a joke and, if it's funny, you enjoy it. But there are other kinds of comedy, like the kind of amateur joking around you do with your friends, where the experience is participatory. Later on, you try to explain the jokes to someone else and, as the words come out of your mouth, you realise how painfully unfunny they are. "You just had to be there, I guess". Or, more accurately, the jokes were only fun to participate in, not to experience passively.
In music, there is a similar effect with jamming. Unless you're some kind of Jimi Hendrix or Miles Davis-level expert, your instrumental noodling is unlikely to be that good to listen to. At the very least, being able to prepare basically guarantees better arranged, better performed music. But jamming is so much fun to participate in that it doesn't really matter how it sounds to anyone else.
The internet has led to a lot of interesting new participatory experiences. For example, the rage comic and image macro phenomena are driven mostly by participation. The simple format and rules for contributing make the barrier to participate very low by comparison to other kinds of content. While it is possible to just consume passively, the best part of the experience is being in on it and making your own.
Interestingly, I don't think anyone has put serious effort into designing participatory experiences yet. The previous examples grew organically out of existing online spaces; they weren't directed the same way you might direct a movie or TV show. Certain avant-garde theatre shows or performance art exhibitions might use participation as part of the experience, but that's relatively rare. It would be really interesting to see something that could provide a fairly repeatable participatory experience in the same way that improvised comedy or music can.
One other thing that I think is worth considering: the success of internet memes as actual memes is really due to how good the participatory experience is. However, there's no reason that is limited to internet memes. If you're trying to spread your ideas, it would be missing the point to make them as entertaining or enjoyable to consume as possible; rather, you want to make them the most enjoyable to participate in.