Six hardware threads, so the thread per subsystem model didn't really work. Instead you got the best results from a DAG of tasks submitted to a job stealing scheduler running on most of the CPU resources. But beside that, no little DSPs that you had to separate work out onto other than the GPU.
And it had the first consumer GPU to incorporate unified shaders (so vertex and pixel shaders ran on the same cores, dynamically scheduled to improve utilization).
They had SMT, but unlike every other implementation of SMT I’m aware of, memory stalls on one thread would stall both threads… which kind of defeats the primary purpose of SMT.
At least with the PS3’s Cell, the SPUs were designed to be esoteric on purpose. It seems like Xenon kind of just ended up being esoteric by accident. (Or maybe they ended up like that because Microsoft were cheating off Sony’s homework)