Fantastic series! I wonder what the general consent is regarding
QTVR versus real-time 3D .. the visuals of Revelation are absolutely stunning at times, but the sense of freedom in realMyst is truly liberating for the genre.
+ There's also a Playstation ( and Saturn ) port of Riven for those who prefer their couch

I think the difference between real-time and prerendered (slideshow/panorama) is pretty profound actually. And I'm not thinking about the visual quality, more the way you explore and experience the surroundings.
A nice analogy here is that of a motion pictures versus still images. We usually only watch a movie once or twice, even if we really like it. But if we like a painting or photograph a lot, we might hang it on the wall and watch it almost every day for the rest of our lives, and still not grow tired of it. That's one single image satisfying you for a lifetime, compared to maybe two hours of twentyfour images per second, which combined keep your interest up only for that time. We're occupied with following the dialogue, story and atmosphere, and couldn't possibly observe every single thing that happens somewhere far in the background in a few frames. But these details would certainly be an important aspect of the experience of a painting or still photograph.
I think there is a similar difference between the fluid, completely navigable realtime 3d worlds, and the more static prerendered environment of the first couple of Myst games. In a prerendered game, a small room might be represented in its entirety as a handful of images, or maybe a single panorama. This is all you get, and as a player you essentially have to assume that everything you need to see will be there, and the opposite - everything that's there will be meaningful to see. I can find myself looking at one single image in a game like Riven for a minute or more at a time, simply because that's the only way for me to really get a feeling for the environment, to scrutinize it.
In a real-time 3d game though, we might treat the environments more like we treat movies. We're less likely to stand still for a minute to look at the world - instead we will move closer to whatever it is that we want to see. Our brains simply have to do a lot more sorting out to cope with the information stream. We get a bit more impatient, we're forced to focus on the whole picture rather than the details, and we may miss some interesting observations.
I'm not saying that one of the experiences is better or more valuable than the other, just that they are different. Obviously, there are all kinds of merits to real-time 3d. But I think it's important to keep these differences in mind when designing the worlds. I think that generally, the prerendered format might work better for very condensed, detailed and information rich enviroments, while the real-time style works best in larger, more open worlds, where
doing is more important than
observing.
In light of this realMyst becomes interesting, since it is a real-time adaptation of a prerendered slideshow game. I agree with you that there is something very liberating about the free movement, but maybe something is lost as well. The pace is different.