Acrylic is half the weight of glass.
It's easier to ship, move, and set up your aquarium.
Acrylic is several times stronger than glass.
It will not shatter, crack, or leak like glass can.
Acrylic distorts much less and is clearer than glass.
If a transparent object is surrounded by another material that has the same index of refraction, then the speed of light will not change as it enters the object. No reflection and no refraction will take place, and the object will appear invisible and without distortion, even at increased viewing angles. In addition to having a slight green tint, glass has an index of refraction that is considerably different from water. Incidentally, clear acrylic plastics have almost the same refractive index as seawater so there is no bending of light as it passes from the plastic into seawater, providing better and brighter color and sharper shapes in acrylic aquariums. The huge viewing windows in large public aquariums and oceanariums can be more than 12 inches thick, but because they are made of acrylic, they afford a very clear view of the water and ocean life they enclose. Acrylic also allows better penetration of your system lighting, which is especially important for reef systems.
Acrylic insulates better than glass.
Acrylic controls water temperature fluctuations, one of the primary reasons for fish stress, disease, and death. Glass conducts heat and cold causing more fluctuations.
Acrylic seams are stronger than glass.
Acrylic seams are molecular bonds and actually stronger than the acrylic itself. Silicone seams used on glass aquariums can dry out and weaken over time.
Acrylic seams are visually superior to glass.
Acrylic seams are polished and nearly invisible. Silicone seams are clearly visible and have been known to discolor when exposed to certain fish medications.
Acrylic is easily refinished.
If glass scratches it can not be repaired. Acrylic can be repaired with a variety of scratch removal kits. Even internal scratches can be repaired without removing the fish or water.
Custom formed designs are possible with acrlylic.
Acrylic can be formed to create interesting aquarium designs which you won't find with glass aquariums.