The first thing I'll note about this style of engagement is that death (or any other form of frequent player failure), is one of the easiest ways to destroy a player's sense of immersion, thus pulling them out of the experience. This is generally something an experiential game does not want to do. That is not to say that there should not be any failure states (Rez, my good example from last time, definitely has them), but that failure states should not be an inevitable aspect of the game.
In an experiential game, a failure state should only occur as a result of a player literally failing at the game. It should occur only because the player has either seriously or continuously messed up, and has fundamentally misunderstood the game's rules. It should be entirely plausible for a player who is not highly skilled to be able to get through the entire game dying rarely, if at all. As an aside, it is perfectly acceptable to have trial-and-error sections, so long as the player is able to undo any mistakes reasonably easily.
The main point that I'm driving at is that an experiential game is not fundamentally about challenge, but immersion. That is not to say that there should not be any challenges (indeed, a game entirely without conflict is unlikely to hold most players' attention for very long), simply that the challenges that exist should be there to reinforce the experience rather than existing purely for the sake of making the game difficult.
Perhaps this should go without saying, but the music and art for an experiential game must reinforce the experience. An experiential game should never have an art style that simply looks "cool" or is technically proficient, it should have an art style that communicates the setting and the experience to the player non-verbally. Colour is one of the most frequently used ways to achieve this, but there are other equally useful ways. Architectural design is perhaps the most important. If the game involves residential areas, for example, everything from the shape of the houses to the style of furnishings inside should communicate to the player something about the world.
I'm not much of an artist myself, but one area that I do have some more experience in is music. Many games today feature music that seems to exist because someone thought it would sound cool; for example, having a choir singing ominous music during boss battles. But is that really the best way to communicate your game world to the player? In some cases it probably is, but you also run the risk of making your boss battle seem like it's the same boss battle players have gone through 20 times already in the past few years. Since what we're going for is a unique experience, this isn't likely to help. We're trying to communicate to players what our world is all about, not how it's similar to someone else's.
For example, in the game I'm currently working on, the narrative is based on themes of social rebellion and the influence of mainstream media. As a result, the music in the game is almost entirely based around punk rock. The soundtrack is also dynamic: distorted guitars and crashing cymbals usually means combat, while clean guitars and more subdued percussion typically indicates puzzle solving. In this way the soundtrack is able to communicate both a sense of atmosphere and information about the gameplay.
Exploration is a vital element of this type of game. This does not necessarily mean spacial exploration. Spacial exploration is definitely an excellent way of allowing the player to truly immerse themselves in the game's world, but in some games this is not entirely possible. Instead, provide the player with the opportunity to explore other things, like the game mechanics. Forcing the player to follow a specific set of actions in a specific order is another way to break immersion. The player spends their time trying to make sure they do everything properly, or like they have no control over the situation.
Here are two examples of ways I have confronted this problem in the game I'm currently working on:
The player's primary tool is a modified guitar that they carry around with them. As a general rule, the player must play clean guitar riffs to solve puzzles, and distorted riffs to defeat enemies. It would make the game far more straight-forward if the background music simply stayed quiet during puzzle sections and became heavier during combat sequences. However, this takes considerable control away from the player. Instead, the background music matches up to the player's decision to play the guitar distorted or clean. This means I've had to find more subtle ways to communicate certain information to the player, but ultimately makes the player feel less like they're being railroaded.
Another, slightly more difficult decision I had to make was whether to require the player to defeat enemies using specific guitar riffs, or using any combination of notes that they would like. In the end, I decided that the player should be able to play any sequence they'd like, as it ultimately allows them to get into the role of the main character far better. I've had to give up some control over the flow of the game and the consistency of the experience, but in the end I'm pretty sure that allowing the player to design their own music makes the experience much more immersive.
I've written the soundtrack in such a way that the sequences of notes available to the player at any given moment will always sound good, so ultimately giving the player this control allows them to concentrate on the experience, rather than on trying to get the correct sequence of button presses entered in time.
Those are some of the most important elements for appealing to this type of player, in my opinion. There are others too, mostly ones that are extremely difficult to communicate using the written word ("atmosphere", for example, is nearly impossible to define in a useful way). I'm curious to hear what other people think are good ways to increase immersion or provide unique experiences, so feel free to chime in in the comments with your own experiences or ideas.