  We present the largest sample of spectroscopically confirmed X-ray luminous
high-redshift galaxy clusters to date comprising 22 systems in the range
0.9<z<\sim1.6 as part of the XMM-Newton Distant Cluster Project (XDCP). All
systems were initially selected as extended X-ray sources over 76.1 deg^2 of
non-contiguous deep archival XMM-Newton coverage. We test and calibrate the
most promising two-band redshift estimation techniques based on the R-z and z-H
colors for efficient distant cluster identifications and find a good redshift
accuracy performance of the z-H color out to at least z\sim1.5, while the
redshift evolution of the R-z color leads to increasingly large uncertainties
at z>\sim0.9. We present first details of two newly identified clusters, XDCP
J0338.5+0029 at z=0.916 and XDCP J0027.2+1714 at z=0.959, and investigate the
Xray properties of SpARCS J003550-431224 at z=1.335, which shows evidence for
ongoing major merger activity along the line-of-sight. We provide X-ray
properties and luminosity-based total mass estimates for the full sample, which
has a median system mass of M200\simeq2\times10^14M\odot. In contrast to local
clusters, the z>0.9 systems do mostly not harbor central dominant galaxies
coincident with the X-ray centroid position, but rather exhibit significant BCG
offsets from the X-ray center with a median value of about 50 kpc in projection
and a smaller median luminosity gap to the second-ranked galaxy of \sim0.3mag.
We estimate a fraction of cluster-associated NVSS 1.4GHz radio sources of about
30%, preferentially located within 1' from the X-ray center. The galaxy
populations in z>\sim1.5 cluster environments show first evidence for drastic
changes on the high-mass end of galaxies and signs for a gradual disappearance
of a well-defined cluster red-sequence as strong star formation activity is
observed in an increasing fraction of massive galaxies down to the densest core
regions.
