I tried mescaline once, however, it was at a very low dose. While it is tough to know the absolute dose as the cactus ended up yielding a load of sludge (it looked like that green TV slime) rather than fine powder, I would ballpark it at a bit less than 100mg (which was then potentiated with 150mg meclobemide). At this dose, it was nothing compared to LSD. It was more akin to naked lysergamide--a very relaxing, mentally upbeat, physically annoying experience. Visuals were light, although I could definitely tell my conscious state was 'altered.' Nausea was present, which really brought down the experience in my opinion. Myorelaxation was fairly intense (I felt a little velcroed to the rug, although not as bad as with DMT). The next day was quite enjoyable, with a significant afterglow similar in character to the aftermath of a psilocin mushroom trip.
It just wasn't as good as LSD, though. I love the utter translucency of LSD--the fact that it is so free of peripheral sides allows it to perfectly "overlay" perception without interfering with cognitive function (at least for me, I know that not everyone has this reaction). With mescaline, I felt "intoxicated," both physically and psychically--everything in the world seemed softer, with lots of HDR-like diffuse lighting. Whereas with LSD, I feel "crystalline," with everything appearing sharper and more "high resolution" if that makes any sense. I guess I also appreciate the stimulant-like "metallic edge" of LSD that people speak about above.