Quantum simulation of spin Hamiltonians is currently a very active field of research, using different implementations such as trapped ions, superconducting qubits, or ultracold atoms in optical lattices. All of these approaches have their own assets and limitations. Here, we report on a novel platform for quantum simulation of spin systems, using individual atoms trapped in highly-tunable two-dimensional arrays of optical microtraps, that interact via strong, anisotropic interactions when excited to Rydberg \(D\)-states. We illustrate the versatility of our system by studying the dynamics of an Ising-like spin-\(1/2\) system in a transverse field with up to thirty spins, for a variety of geometries in one and two dimensions, and for a wide range of interaction strengths. Our data agree well with numerical simulations of the spin-\(1/2\) model except at long times, where we observe deviations that we attribute to the multilevel structure of Rydberg \(D\)-states.