A mixed bag really. I hate the pots. I read a lot about them but thought it was the usual reaction to change. No, they actually suck. They are fine as long as you double check they are shut but it's quite easy to think you close one but haven't quite. I also dislike the little tag that helps them stay open. There is no need for that at all.
They are also not the best value out there. P3 are great value and really nice. Plus they come in better pots (much like the original citadel pots from when I started out). GW have never been big on value though. I knew that so can't complain. I made that choice and I'm happy because...
...the pigments are, with a couple of exceptions, very nice. They are thick and saturated and take to being diluted very well. I use distilled water and have found they thin very well and take a while to separate. I've recently started using a wet palette as well and they work very well with it. The inks are excellent but GW inks have always been good. The glazes are also very nice and it is easy to get a flat smooth coat. Only four but you can pretty much mix what you like with them.
My only gripe with the pigments are a couple of the colours aren't so good. I was always a fan of bleached bone and used it for a lot of warm highlights. Ushabti is no way near as good. It's granula and dries too fast and, along with pallid wych and screaming skull, seams to separate a little.
Lahmain medium is great for two things. It can be added to inks to reduce the shine you can get from a wash and it is great for making glazes out of regular paints (with water too).
The drybrush colours all look too pale in the pot but work really well.
Textured paints. Hmm. I've not used them seriously yet, so will withold judgement.
Imperial primer. Utter rubbish. It pools nastily, separates fast, takes an age of shaking to mix right and worst of all doesn't cover properly. It's not even any use to touch up where spray undercoat has missed. A thin coat of abaddon black is much better.
All in all though I am really pleased with them. I do think you could buy the set and not need any other colours. I've seen a few people rant about the eavy metal edge set. I can see why but really you don't need to buy it. You can make any of those from the rest of the range but it's convenient. I may even buy a set myself, as I do often mix a very bright highlight for edges.
So that is my mini review. I'm in favour, with a few exceptions.
I will still buy a few P3 and Valejo pots now and then. Not because I need to but because some colours are available that I would mix and it saves me time. FOr a couple of pounds that is worth it.