Itanium wasn't x86 compatible, it used the EPIC VLIW instruction set. It relied heavily on compiler optimization that never really materialized. I think it was called speculative precompilation or something like that. The Itanium suffered in two ways that had interplay with one another. The first is that it was very latency sensitive and non-deterministic fetches stalled it. The second was there often weren't enough parallel instructions to execute simultaneously. In both cases the processor spent a lot of time executing NOPs.
Modern CPUs have moved towards becoming simpler and more flexible in their execution with specialized hardware (GPUs, etc) for the more parallel and repetitive tasks that Itanium excelled at.
