The Cooler Master HAF Stacker is by no means reinventing the wheel as other case brands have been offering enclosures with the ability to hold two separate systems. But Cooler Master has managed to refine the concept behind doing so well by taking it from being a niche product and making it something with mainstream appeal. The fact that you are able to easily detach the two compartments to rearrange things within the case add to their refinement. Yet Cooler Master was not as thorough as I would like as there is no possibility to turn the second system inside the smaller chassis on without going out and buying an accessory, for example. The entire chassis, top and bottom, also only ships with two basic fans. In a perfect world, the larger chassis should have shipped with two more cooling units in the front. Next, the smaller unit in the set should have been a fully configured 915R since Cooler Master refers to it as such in their specifications table. Those last two points keep this case from moving past our Recommended award. That said, look past those points and the HAF Stacker is actually a very good chassis as it sports loads of room for parts, very good cable-management possibilities, easy and tool-less installation methods, and the flexibility to install big components and an elaborate liquid-cooling setup. Cooler Master even managed to ensure that the smaller chassis can not only be used for a secondary system, but as a storage compartment for hard drives or you water-cooling gear.
Overall, it, even though the HAF Stacker manages to catch the attention of a much larger audience than any other chassis of this type, does still remain a bit of a novelty to have. It might have been best to offer the larger chassis in a fully functional configuration on its own for around 129 US dollar to then sell the 915 units separately instead of forcing users to buy the HAF Stacker as it is right now - as its current configuration limits its potential user base.