Accurate measurements of the properties of galaxy clusters are a vital tool in modern cosmology, providing a unique insight into the non-linear regime. Previous works investigating biases in measurements of cluster observables using numerical simulations have either been restricted to dark matter only simulations or have been limited to a small number of high-mass clusters. The MACSIS project is a set of hydrodynamical simulations of massive galaxy clusters which extends the cosmo-OWLS sample of galaxy groups and less massive clusters to higher masses. These simulations use the sub-grid physics models developed in the cosmo-OWLS project, which includes feedback from supernovae and active galactic nuclei. Taken with the cosmo-OWLS sample, the simulations form a population which covers almost two orders of magnitude in mass, with more than 170 clusters with masses greater than 10^15 solar masses at z=0. This sample is used to determine the scaling of the concentration, spin and shape of high mass clusters with mass. Mock shear and convergence profiles for the clusters are used to quantify the influence of substructure and halo shape on weak lensing mass and concentration estimates.