^ Funny you ask, I actually had it IVed a couple of weeks ago for endoscopy. It wasn't particularly thrilling. I just felt like my thinking was being slowed down at a very high rate, and maybe slightly relaxed (but then again I was experiencing traumatic anxiety at the time, AND had a high tolerance).
onmyway: phenaz is definitely not the best choice for a first-time benzo experience. It is pretty weird in its action and someone who doesn't know what to look for may get very lost on it.
I think the only thing stopping phenaz from becoming a premier drink-spiking drug is the fact that it is so poorly soluble.