Metals have several general properties in common (to some degree):
All of these properties derive from the "metallic bond", a delocalized sharing of electrons throughout the metal lattice, which is the key necessity for displaying macroscopic metallic properties. All metals do not behave the same way for these properties. For example, gold is more malleable than iron.
Metalloids are those elements with one or more allotropes that have metallic characteristics. Few if any metalloids display all of the metallic characteristics (otherwise they would be metals!). For example, graphite is lustrous and electrically conductive, but not thermally conductive, malleable, ductile, or fusible. The metalloid with the most metallic behavior is tellurium, which is fusible and ductile.
As for compounds, many are like the metalloids - they have some properties of metals but not all. For example, silicon carbide is lustrous, but that's about it. Otherwise it is hard, brittle, and an insulator.
Polyacetylene and derivative polymers are sometimes call "synthetic metals" because of their electric conductivity and sometimes luster. However, again, they are thermally insulating. They also tend to burn instead of fuse.
Metalloid elements and compounds are not quite metallic because their electron delocalization is in only one (polyacetylene) or two (graphite) dimensions, not all three.
Based on Snipergirl's comment, it appears that we are closer than I originally thought to preparing true synthetic metals. This highlight at phys-org suggests that supramolecular lattices of redox-coupled conjugated organic ions can exhibit metallic behavior at low temperature. The full article is at Nature Communications and has been made open access. These compounds appear to be close to achieving delocalization in all three dimensions. The behavior of this organic material is not surprising: metals and metalloids become even more metallic at cryogenic temperatures. The induced superconductivity allows for such cool things as magnetic levitation and MRI.