Isotropic conductive adhesives will conduct electricity in 3 dimensions. These products are formulated to contain very high filler loadings - up to 35% by volume. The goal when formulating isotropic adhesives is to load the resin such that the filler particles are able to touch and provide a direct electric pathway (Remember epoxy and most polymer adhesives are electrically insulating). To this end, isotropic adhesives are normally formulated with long plate shaped particles.
Anisotropic conductive adhesives, on the other hand, are formulated to exclusively provide electrical conductivity across the bondline. Filler loadings are reduced (to about 1-5% by volume) and fillers are normally spheres with a diameter the exact thickness of the intended bondline. In this way, when the the interface materials are pushed together the bondline is reduced so that the filler particles make contact with both materials. Anisotropic adhesives are typically less costly (due to the reduced percentage of metal fillers), but require a precision assembly process.