We investigate magnetic reconnection and particle acceleration in relativistic pair plasmas with three-dimensional
particle-in-cell (PIC) simulations of a kinetic-scale current sheet in a periodic geometry. We include a guide
field that introduces an inclination between the reconnecting field lines and explore outside-of-the-current sheet
magnetizations that are significantly below those considered by other authors carrying out similar calculations.
Thus our simulations probe the transitional regime in which the magnetic and plasma pressures are of the same
order of magnitude. The tearing instability is the dominant mode in the current sheet for all guide field strengths,
while the linear kink mode is less important even without guide field except in the lower magnetization case.
Oblique modes seem to be suppressed entirely. In its nonlinear evolution, the reconnection layer develops a
network of interconnected and interacting magnetic flux ropes. As smaller flux ropes merge into larger ones, the
reconnection layer evolves toward a three-dimensional, disordered state in which the resulting flux rope segments
contain magnetic substructure on plasma skin depth scales. Embedded in the flux ropes, we detect spatially and
temporally intermittent sites of dissipation reflected in peaks in the parallel electric field. Magnetic dissipation
and particle acceleration persist until the end of the simulations, with simulations with higher magnetization
and lower guide field strength exhibiting greater and faster energy conversion and particle energization. At
the end of our largest simulation, the particle energy spectrum attains a tail extending to high Lorentz factors
that is best modeled with a combination of two additional thermal components. We confirm that the primary
energization mechanism is acceleration by the electric field in the X-line region. The highest energy positrons
(electrons) are moderately beamed with median angles  30° - 40° relative to (the opposite of) the direction of
the initial current density, but we speculate that reconnection in more highly magnetized plasmas would give
rise to stronger beaming. Lastly, we discuss the implications of our results for macroscopic reconnection sites,
and which of our results may be expected to hold in systems with higher magnetizations.