What is a good CPU cooling system?
The same as to any cooling system, but the manufacturer has to find an optimum balance between the parameters of the good liquid cooling system and the manufacturing cost. For example, a larger heatsink improves heat transfer, but this contradicts the compactness requirement; a more powerful fan would make the system noisier, etc. This is a difficult task and the developer has to agree to compromises. The market success of a liquid cooling system depends on how optimal the result is.