Yeah, we checked it out when we first got my Rift and it was crazy. I'm fairly certain I know what site you checked out (as THAT Riley video was kinda the standard flag-bearer for what the industry could do in VR) and they tend to get the scale, the intimacy, and actual feeling of what it's like to be there too.
As for my (and by proxy, my wife's) impressions:
VR has the potential to be an absolute game changer for the adult sector. Sure, it's still in the very early phases of figuring things out and there are a couple key problems (scale, clarity, lack of 360 degrees, etc) but there are some sites out there really pushing the envelope.
For me, the biggest difference between this and traditional stuff is that a large proportion of traditional videos are more voyeuristic; you're watching in on something and you're relatively detached. Even with POV stuff, it really more fees like "oh it's the camera guy that's nailing the actress" rather than you. VR completely demolishes this and gives you a completely new experience. Now, at its best, the porn VR companies are realizing they no longer are selling a voyeuristic experience but are selling closeness, intimacy, and essentially a Girlfriend Experience. Things that you couldn't give a shit about before like positioning, eye contact, and so forth are the things that you notice immediately. There were videos where an actress goes in for a kiss and I reflexively back up since I was sitting next to my wife and it just felt too real. In addition, more than ever things like bad acting or fake performances stick out immediately.
Having said that, there are a number of issues. Scale is something that some sites are still having trouble with, and sometimes videos feel more like Death by Snu-Snu. Similarly, the resolution is still fairly low for a lot of sites, and most sites are still doing only 180 degrees, meaning you look too far to the left and right, you're gonna see black and you're immediately taken out of the scene. But these are issues that the industry will certainly figure out as the technology improves.