Just picked up a used one from craigslist, for $80 and it's so much better then all the crappy chairs I've had in the past, and pretty adjustable. Almost a better upgrade then a mechanical keyboard.
Don't really have any experience with nice chairs so I can't really compare but either way it was a steal at this price.
Arm rests adjust up and down, front to back and pivot in and out, along with and adjustable bottom that slides back and forth and reclining knob to adjust how far back you can recline, that's easily reachable while sitting. Also has an adjustable lumbar support.
The mesh is supported by flexible wire to conform to your shape. Doesn't seem like it would fit larger people to well though, but I guess no chair that comes in one size will fit everyone.