For me it was "broken", especially when you compare it with the older Hitman. I played on purist and the disguise system was completely useless. I could've lived with something like H2 where you can't run in front of enemies without making them suspicious about you... but here they get suspicious even if you're surrounded by dozens of people. I don't know if they patched it though.
How's the stealth system in Mark of the Ninja? by the look of it I thought that it was simplistic, but I didn't installed it yet.
I cannot imagine why anyone would play on purist their first time. Games are mechanical systems and it has to be nigh impossible to learn the systems by turning off all the information conveyance your first time. Once you figure out that thrown item distractions are mechanical and always have the same effect on the AI the game becomes a lot easier.
I don't know why they would patch it. That disguise system is entirely intentional and an integral part of the gameplay. The levels would be hilariously easy if a disguise just let you walk through.
Mark the Ninja was elegant. That's the way I would describe it. Sights, sounds, shadow, and acrobatics. It just works really well.