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Fresnel reflections (on the left) compared to uniform ones (on the right); in the Fresnel case, note how the reflection fades off as the angle between the eye vector and the surface normal decreases
Whatever the model you choose, reflections can be made glossy and / or anisotropic. The glossiness is a measure of the dispersion of the reflection rays around the perfectly specular reflection vector. It can be seen as the half-angle of the cone subtended by the reflection vector where reflection samples are taken. The more the angle increases the more the reflections are blurry (and will require samples to avoid too much noise; see figure below).
The sphere on the left right is less glossy than the one on the rightleft.
The anisotropy defines the shape of the reflections. Anisotropic materials reflect light according to the surface orientation (see figure below). It means that a local surface coordinate system is needed to handle oriented reflections.
The sphere on the left is isotropic as the one on the right is anisotropic. Notice how reflections are vertically distorted in the anisotropic case
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