What is remarkable about fuel cells?

The only thing that comes out of the tailpipe is water! The other not so remarkable thing is the price.
A fuel cell is made up of two electrodes, and each one is an ion-transfer membrane (allows ions to pass through but not air or liquid). In between these membranes is a liquid called electrolyte, whose job is to carry ions from one electrode to the other. On the far side of the cathode (negatively charged electrode), hydrogen is pumped in, and on the far side of the anode (positively charged electrode), oxygen or air is pumped in. At the cathode, hydrogen is stripped of its electrons, which get removed by the electrode. This electricity is used to power lights, ovens, computers, etc.. The remaining hydrogen ions flow through the electrolyte and converge on the anode. On the return trip the electrons get fed into the anode where they are picked up by oxygen atoms, which then combine with the hydrogen ions to form water. Viola, you have a fuel cell.

The reason they are so expensive is because, at the anode, a catalyst such as platinum has to be used to help the reaction along. The other issue that is preventing widespread use of the fuel cell is that an effective hydrogen distribution system is not in place. You could have a fuel cell car, but where would you buy hydrogen?