The finish of the YSL Glossy Stains reminds me of the Lip Ink system (I reviewed that here: Lip Ink Fire Red) except that the clever folks at YSL have got the stain and the glossy top coat all combined in one tube.
One coat gives an even stain with glossiness that lasts a good couple of hours. The stain remains after the glossiness has faded, although it looks less vivid without the sheen of the gloss, and it has faded considerably after three hours of wear (see my pictures below.) Reapplying to refresh the glossiness builds up colour, which is fine if you want to build up colour but not so good if you just want to refresh the glossiness although you could just use a clear gloss to do that.
Adding a second coat intensifies the colour density and glossiness, although to me it feels uncomfortably gloopy and I'm happier at one coat (I almost never wear lipglosses because I can't stand the sticky feel of them though, so it's worth taking that into account.) These are sticker than Chanel Rouge Allure Laques or Beaute Weightless Lip Cremes, but they are a different and glossier finish, and do tend to wear a little better in my opinion.
The delivery system is quite alcohol based (also like the Lip Ink) and you can feel the alcohol when you first apply it. The new, whizzy, wand applicator thing is actually quite good, although I do find it can deposit too much colour at the edges of my lip, which I need to blend down with a fingertip or separate lipgloss. Glossy Stains have the same perfumed rose scent of the Rouge Pur Couture lipsticks.
I bought 01 Violet Edition, which is a plum shade that's very slightly to the violet rather than brown side of plum to my eye. There are 20 colours in total, from nude to red and most shades you'd expect to find in a lipstick range.
Picture with one coat applied:
Second coat applied. It's not much deeper or darker, but it is more intense and glossier (and stickier.)
One coat after 3 hours, a cup of tea and breakfast (complete with stray hair.) There is still colour, but the glossiness is gone and the colour faded. If you eat or drink, don't expect it to look like picture one for more than an hour or two. It hasn't dried out my lips though, and it has left a stain (my lips fade into my skintone when bare.)
Picture in context of the rest of my face (with one coat freshly applied.)