These are pretty standard liquid eyeliners, but the best thing is that they come in so many different colours. The brightly coloured liners are very pigmented and go on opaque, which is more than you can say for cheaper brands doing the same thing. (I have the gold and the lime green Lime Crime liners).
Unfortunately these are pretty hard to get your hands on as they are fairly inconsistently stocked and the Lime Crime website doesn't seem to carry them at all - so they might be discontinued? They are really bright and the metallic ones are very shimmery so they are definitely worth tracking down if you can.
My favourite thing about these liners is the amazing color range. I have used the black and the purple and would absolutely try pretty much every other color. I also really love the teeny little brush which makes getting a perfect cat eye easy. They definitely are not anywhere near waterproof and can transfer quite a lot, so are pretty high maintenance, but I find for special occasions it's just worth it. The bottle is very small, much smaller that I expected but a little does go a long way, and as always for lime crime products, the packaging is gorgeous and gets pride of place on my dresser.