I tried Salvia for the first time last night, and had a level 3, bordering on level 4 experience.
It is kind of like everything and nothing at the same time.
My first 10 minutes or so were full of closed eyed visuals coupled with strange body sensations of gravity bending, and being fluid rather than solid. I also sensed the presence of others, and heard their song, but only saw them as shapes and impressions rather than full out images.
The next two hours of the trip were euphoric and full of self discovery. I wound up meditating on each of my chakras, which told me stories about myself and what I need to do to honor them. I constantly felt the connection of everything in the universe and the presence of divinity. I have been in similar states before, on mushrooms, ecstasy and lsd, as well as doing an open eyed chakra meditation while stoned.
I think that people's varying reactions to salvia has a lot to do with the place they are at in their lives and in their spiritual and intellectual development.
I think that in order to have a positive experience, you have to be at peace with yourself and your life, secure with your place in the universe and have a very innate understanding that the boundaries of reality that we normally see are just an illusion. If you are not ready to let go of your boundaries, it would be a terrifying experience.