I've only had one massage that was advertised as tantric (my first ever review here!) and I can say it was a different experience to the usual rub and tug you associate with regular FBSM.
I don't know if this is true across the board but I definitely got the impression that it was more of a meditative affair, with less interactivity encouraged and more passivity as the SP works things to a climax. Whether you'd entertain calling it a spiritual experience or just a damn good edging session is subjective, but I've done a little Tai Chi in the past and some of the sensations were reminiscent.