Most people are saying that it is not silent and that you an get quieter fans that shift the same amount of air.
Whilst this is true you must remember the difference, most fans has more blades but thinner.
This fan has a few large blades, this makes a HUGE differenced, this fan will shift more 'static' air.
What this means is that this fan shifts the air in more scenarios, like if you have water cooling, this fan will pull or push the fan through the radiator better. If you use dust filters or have a small or cramped case then this fan will still shift the air.
Also as the temperature increases there will be pressure changes inside the case, this fan will perform better then a fan with thin blades.
In short, this is a good fan that will operate well where other quieter fans do not, but it is loud, if noise isn't an issue then this is the fan for you.