There is one word that really helps sum up what radiant heat flooring is all about - toasty. It is that feeling you get when your feet are lovely and warm when all around you the winter is biting - snow or ice or dirty sludge on the ground.
Any kind of radiant heat floor will give you this feeling, but not all systems are the same. Some are designed to be your source of heating for the home, others are designed to supplement another form of heating and to simply provide you with that toasty feeling.
There is no hard and fast rule of course, and what in the North East of the US might be little more than the supplementary warming systems electric floor heat provides may, in Southern Florida for example, suffice for year round heating.
Generally speaking electric floor heat is easy to install (a series of carpet like strips that fit beneath the carpet), gives a fine warm sensation and a nice heat throughout the room. For people with cold winter though they might not work out to be the most cost efficient systems. This is because electricity costs more, as a heating producer, than some other fuels.
Hydronic radiant floor heat systems are, in general, more of a hassle to fit, but are more likely to be able to cope with winter conditions that are colder. Since they involve using some fuel (gas, oil, wood, coal) to heat water and pump it around pipes underfloor, you do need to have a boiler installed and pipes fitted beneath the floor. But this investment can prove really worthwhile, offering you year round toastiness.