I've got a bunch of the ByKilian ones for sale and someone PM'd me to ask about them, so here's how I described them:
I think they have most of the same scent as the actual perfume. The smells never translate across forms (lotion, wash, solid, candle, etc) perfectly, but are to my nose roughly the same. Top notes are so fleeting anyway in perfume, which is not to say that the solids don't have them, but I wouldn't get too hung up on them. I find they act more like a pure parfum, ie much lower sillage, sort of a hovering few inches above the skin, and pretty good longevity, like 6-10 hours.
What's probably the most different is how it wears on the skin. To begin, instead of the smell being carried in alcohol, they're in a solid form. The consistency is like an oily 'wax', when cold it's a bit firm like a soft candle, when rubbed on and into the skin, I'd say it's closer to vaseline. It's not at all sticky anything, sort of like a natural oil or gel for lack of a better description. It's sort of more an natural way to wear perfume in the sense that it seems to meld with the skin and become more a part of the wearer. To apply, basically you just rub your finger in the container and rub it into your skin (wrists, chest, behind ear, back of neck, etc).
It's a unique form and very few lines do it so I think it's pretty interesting and in the case of ByKilian, I believe they are being discontinued.