Best use case for 120mm AIOs IMHO is if you've got a side window in a compact form factor and you'd like to be able to show off your internals without being dominated by a heatsink, or if you're shipping a system and don't want the possibility of a giant heatsink breaking the mobo while it is being transported. A quick look at benchmarks indicates that it performs decently at low fan RPMs, but you only get its best performance at a fairly high noise cost.
So it's fine for what it is. What are your expectations for it?
Actually, I've been concluding for some time now that the noise issue is a myth.
Everybody probably snickers at my choice of an AP-30 fan as combination exhaust and heatpipe-tower puller. And if you look at the top-end noise rating for that and some other similar fans, it seems totally unacceptable.
One of my AP-30's has an acoustic duct to the rear exhaust. It's the noisier of the two -- I just recently discovered. But below 3,200 RPM, it ranges between "can't hear it at all" to "just barely . . . hear . . . something." With the less-noisy of the two AP-30's, there is no need to attenuate the noise with acoustic dampening materials.
What I discovered while tuning my "new" 2700K system was this. While adjusting voltages and speed for stability, I let the AP-30 ramp up to its full top-end 4,200 RPM -- still disciplined by a fan-curve of the ASUS "Turbo" profile. Once done, the reduction of maximum RPM by ~1,000 RPM in a custom fan-curve profile means a 1.5C increase in IBT temperatures. Suppose my IBT temperatures were 68.5C, measured either by the four-core average of maximums or the prevailing "package" temperature. Then reducing the fan-speed to maximum 3,200 RPM by changing the fan-curve and profile means my IntelBurnTest "Maximum"-level temperature will be ~70C -- which . . . it is.
Generally, your temperatures under gaming aren't going to reach this level if the best IntelBurnTest can do is 70C. So I can't imagine more fan noise than one would expect with a water-cooled system using two to four fans for a 280mm radiator with additional intake fans that would only make sense. At most, there might be "white-noise" from air-turbulence, but what I hear faintly is the resemblance to the ceiling AC vent in a room during a summer day. And that "white-noise" only occurs for the no-holds-barred stress-tests of LinX and Intel Burn Test.
There are better fans than the AP-30 (Gentle Typhoon). For instance, one model of a Noctua 120mm PWM "iPPC" fan tops out at 3,000 RPM. The fan is virtually noiseless given the maximum temperatures under stress. A person could really improve cooling effectiveness on a double-radiator with the iPPC fans.
IMHO, the obsession with fan-noise has driven people to water-cooling, only to embrace greater cooling efficiency and effectiveness while the noise-reduction over air-cooled fan choices is insignificant if any reduction at all. Conversely, improving the fan, adding a duct, pressurizing the case only increase air-cooled efficiency (or radiator effectiveness), but the result can be thermally-controlled to eliminate the fabled noise.
The caveats about fans require the attention to details that once prevailed in the forums with a "DIY" spirit. Don't mount the fans with metal screws; use rubber fan mounts; avoid any contact between fan-plastic, metal fasteners and chassis metal. this would especially hold true for radiators, which will otherwise amplify transmission of noise or vibration through the fan-frame and shroud. Especially, for radiator mounts, it's important to choose fans that lack motor noise -- whines or "whistles" -- because those noises will also amplify in radiator fins.
But there's no reason to avoid higher CFMs or airflow under higher temperatures. I think it is therefore self-defeating -- to avoid minor white-noise of air turbulence at high temperatures when those temperatures are seldom reached in normal usage. None of the AiO coolers shipping these days are equipped to take advantage of the full cooling power of their radiators. And that may be part of an unbalanced obsession with noise that is avoidable anyway.