Ok, so I took advantage of 20% off the price they are offering and subscribed for one month... being the first porn game for the Rift and all.
For science

So, what it's like?
I didn't use any of the chat funcions yet, just tried the AI bot.
First the good stuff.
Graphics look really great in VR and while not technically too advanced, they are still some of the best I saw in erotic game (penetration is very nice).
I walked around a bit an then chose sex on bed. Well... Oculus Rift is quite a magical toy and I can say it really feels like you are an invisible man watching a couple having sex in all their life size glory. As I noticed in other demos with characters, you feel their presence and getting really close to the girl is very sexually arousing- something I have never experienced with 3d xxx games on monitor (I failed to seize what's so good about polygon tits. It all just felt awkward).
In a few sex positions you can actually fake first person view and I can already say it will be quite powerful. I think, coupling this with V-Stroker could be amazing.
I have a mild foot fetish. And while 3d pollygon feet on monitor don't look all that inviting (compared to the real stuff

), Rift does its magic again and, while looking up close, feet look "real" and sexy.
What about the negatives?
First, there's no first person view. FPV is a must as it elevates immersion factor through the roof! Third person should stay as an option (it can be nice, to feel like an invisible voyeur).
Second, HUD is not adapted to VR at all. You must take off Rift to use options, which is a huge immersion breaker.
While having sex, faces are hardly animated. That's one thing you really notice in VR. It would be nice to have some pleasure animations (moaning, lip biting, breasts grabbing, etc.). And sex could be made with a bit more variety- not just continuous loop but with a few special stuff thrown in here and there.
I'd also love to see animated transitions between poses. Right now characters just switch to new positions.
It would be nice to have more options for character design. All characters look more or less the same and it would be cool to have some more variety.
In future, posing a girl yourself (grab her legs, etc. (similar to Xmoon game)) would be a great option.
Anyway, I can already say that sex games in Rift have a really bright future. They can actually make you genuinely horny. Even experience of sex alone, without story and other interactions, can be enough in VR. I can only imagine what it will be like, once the tech and software advance. Mindblowing!
So is 3DXchat worth 20$?
Without the Rift, I would have to say no. If you have Rift, it depends. If you are like me and just want to get a taste of what porn games feel like in Rift, then yes! If you want polished VR experience (HUD, FPV), with lots of options, different environments, interaction possibilities (etc.), then no.
In any case, I really hope, authors will rethink their price point and offer the game for 10$ a month, or as a one time purchase for a bit higher price. They'll get more users and the game like this can only benefit from that.