In short, I like them, more than I thought I would. It’s not that they are significantly better than Vallejo (my preferred paint until now) simply as paints - they certainly are not the better of Vallejo in areas like coverage, pigmentation or ease of application. In fact, in many of these areas, I would prefer Vallejo over Foundry. As paints tout court, the Foundry paints are good, but they are not significantly better than anybody else.
What I do like about the Foundry Paint System is what makes it a System, no matter the slightly presumptuous sound that may have. It’s the fact that the paints come in sets of three — shade, base colour and highlight — that makes this line of paint so good. Despite the advantages of mixing the highlight colours from the base colour I stated earlier, it remains a somewhat hit-and-miss affair, which you no longer have with the FPS. This is reason enough for me to gradually make the switch to the Foundry Paint System: you always have your highlight colour available, even if it is a colour someone else chose for you. And it is the highlight colour that goes a long way to making or breaking a three-layer paint job.
Additionally, just painting with the paints and seeing them face-to-pigment has taught me something which I had not appreciated before: the shade colours are actually fairly light in value, corresponding more or less to the lightness of the base colours I am accustomed to use. Part of what makes a Foundry three layer paint job look the way it does is just that: the shade colour is already fairly light, which brings about a good contrast between it and the black prime coat (black priming becomes essential for this). I had not appreciated this before, but I can already see me migrating towards this style a bit more (which will be automatic with the FPS anyway).
In short, if anyone is looking for a Christmas present for me, pallettes 3, 4 and 10 are next on my list :).