The quantum-classical crossover from the Fermi liquid towards the Wigner solid is numerically revisited using small square lattice models where electrons interact via a Coulomb U/r potential. From exact numerical diagonalizations, one finds that the mesoscopic electron solid is formed in two stages, giving rise to an intriguing solid-liquid regime at intermediate couplings. The roles of a random substrate and of the spin degrees of freedom are investigated. Possible relations with the 2d metal-insulator transition observed in various field effect devices are suggested.
