  We report on a systematic study of the thermodynamic, electronic and charge
transport properties of high-quality single crystals of BaNiS$_2$, the metallic
end-member of the quasi-twodimensional BaCo$_{1-x}$Ni$_x$S$_2$ system
characterized by a metal-insulator transition at $x_{cr}=0.22$. Our analysis of
magnetoresistivity and specific heat data consistently suggests a picture of
compensated semimetal with two hole- and one electron-bands, where
electron-phonon scattering dominates charge transport and the minority holes
exhibit, below $\sim$100 K, a very large mobility, $\mu_h\sim$ 15000
cm$^2$V$^{-1}$s$^{-1}$, which is explained by a Dirac-like band. Evidence of
unconventional metallic properties is given by an intriguing crossover of the
resistivity from a Bloch-Gr\"uneisen regime to a linear$-T$ regime occurring at
2 K and by a strong linear term in the paramagnetic susceptibility above 100 K.
We discuss the possibility that these anomalies reflect a departure from
conventional Fermi-liquid properties in presence of short-range AF fluctuations
and of a large Hund coupling.
