28mg wasn't significantly different than 18mg for me. I'm not sure if I reached the point where if I took more it would only elongate and not intensify the trip. It took me as far away from my sober self as weed or alcohol but in a different direction.
Mental effects were quite mild and the only visuals I initially experienced were a slight saturation in colors. Later, when I thought the trip was coming to a close, I noticed movement in a stationary towel. It was like when you cross your eyes and stare at those images to get an outline of a 3d object. To get these you would have to let your eyes slightly blur and rest on one spot, a bit like when I tried acid but less intense.
As neat as this was, the best happened when I was laying in bed with the lights turned off. The pattern-recognizing part of me was unrelenting in making sense of the noise of the dark. Walls weren't a continual shade or gradient of gray, but somewhat like the static or 'ants' from a tv screen. The colors were like those of my closed eye although I kept my eyes open. My mind would shift between visuals styles from intricate isometric geometries to fractals and tessellations. I would see a style used for an album cover and then something abstract resembling repetitions of architectural drawings. These images weren't completely clear, having the clarity of remembering someone's face more than looking at it in real time. I was amazed at how effortless they came and wished I could draw them. This went on for maybe two hours.