  We investigate the properties of the intracluster medium (ICM) that forms
within N-body/hydrodynamical simulations of galaxy clusters in a \LambdaCDM
cosmology. When radiative cooling and a simple model for galactic feedback are
included, our clusters have X-ray luminosities and temperatures in good
agreement with observed systems, demonstrating the required excess entropy in
their cores. More generally, cooling and feedback increases the entropy of the
ICM everywhere, albeit without significantly affecting the slope of the profile
(S prop. to r) at large radii. The temperature of the ICM is only modestly
increased by these processes, with projected temperature profiles being in
reasonable agreement with the observations. Star/galaxy formation is still too
efficient in our simulations, however, and so our gas mass fractions are around
60 per cent of the observed value at r_{2500}. Finally, we examine the
reliability of using the hydrostatic equilibrium equation to estimate cluster
masses and find that it underpredicts the true mass of our clusters by up to 20
per cent, due to incomplete thermalisation of the gas. Feedback reduces this
discrepancy, however, with estimates being accurate to within 10 per cent out
to r_{500}.
