  Recent years have seen an increasing interest in quantum chaos and related
aspects of spatially extended systems, such as spin chains. However, the
results are strongly system dependent, generic approaches suggest the presence
of many-body localization while analytical calculations for certain system
classes, here referred to as the ``self-dual case'', prove adherence to
universal (chaotic) spectral behavior. We address these issues studying the
level statistics in the vicinity of the latter case, thereby revealing
transitions to many-body localization as well as the appearance of several
non-standard random-matrix universality classes.
