Home planet of Glil.
Most of the chemical reactions that life relies on take place within a watery environment. Water dissolves many different molecules — it is a solvent, and having a good solvent is a prerequisite for the kind of chemistry that brings about life.
Like water, ammonia is also common throughout the galaxy. It's also capable of dissolving organic compounds like water, and, unlike water, it can also dissolve some metallic ones, opening up the possibility for some more interesting chemistry to be used in living things.
However, ammonia is also flammable in the presence of oxygen; has much lower surface tension than water, making it difficult to hold prebiotic molecules together for very long; and its melting and boiling points are much lower than water, at –78°C and –33.15°C, respectively. Thus, the chemistry of ammonia-based life would occur much more slowly, and commensurately, its metabolism and evolution would also be slower. An important caveat, though, is that these are the melting and boiling points that occur at Earth's atmospheric pressure. Under higher pressures, these values would rise.
One of the exciting features of ammonia-based life is that it could exist outside of the so-called habitability zone, or the range where liquid water can exist. Titan, for instance, may hold oceans of ammonia beneath its surface, and although it lies outside of our solar system's habitable zone, it could for this reason host life. Astrobiologists often point to Titan as a possible site of alternative life forms within our own solar system.