The internals of the Corsair Obsidian Series 750D is certainly big and should suffice for most enthusiasts. Depending on how you configure the HDD cages, the case will easily swallow graphics cards from 340mm to 460mm in length. So unless you have a radical aftermarket cooler on your graphics cards, it should fit with no issues. The case will also accommodate CPU coolers up to 180mm in height.
Installation is largely a tool-free and straightforward process. Optical drives can be slid into their respectively bays and then locked into place by using a latch. 3.5-inch hard disk drives can installed simply by placing them into the HDD trays and then sliding into the HDD cage. 2.5-inch drives can also be installed within the HDD cage, but that would require screws, better to just use the SSD caddies - they fit 2.5-inch hard disk drives too. In addition, the expansion slots are held in place by thumb screws, which can be removed by hand. The only time you would need to reach for a screwdriver is when you are installing the motherboard.
Corsair offers a fair degree of customizability in so far as cooling options and HDD cages are concerned. The 750D comes with three fans (two front, one rear) and users can opt to install an additional fans on top or at the bottom of the casing, or use the mounting points for installing radiators for their liquid cooling setups. The 750D can accommodate up to 240mm, 280mm and 360mm at the top; 240mm radiators at the bottom; and up to 280mm radiators up front in place of the standard two front intake fans..
The two HDD cages, which hold a total of six drives (both 3.5 and 2.5-inch) can also be shifted and rearranged. By default, the two cages are installed at the bottom side by side, presumably to allow unrestricted airflow from the front intake fans. However, they can also be stacked on each other. If you are opting for only SSDs, they can also be removed entirely, because there are four SSD caddies on the flip side of the case. These caddies are specially designed for SSDs - simply slid them in and they will be locked in place.
As you can see from the photos below, the PSU bay is only just about large enough to accommodate our 750W PSU. For users with larger PSUs, this would mean that they would need to reconfigure the layout of the HDD cage and remove the HDD cage mount. The HDD cage itself is easy to remove - just undo two screws and slide the cage out - but the mount itself requires the user to undo four screws at the bottom of the case.