As far as side panels go, the design is classic. The left panel can take a 140mm or 180mm intake fan, while the right panel has no holes. Both panels are fixed with thumb screws and taking them off is as easy as putting them back on. The panels are made of steel and are very tough.
The top panel is made entirely of mesh. Users tend to keep random things on a case and it's possible in this case as well since the panel is flat and the mesh is tough enough. Of course, that won't help much if you spill something.
The top panel houses a 140mm fan, but there is extra room for two additional 120\140mm fans. The top panel can be removed after unscrewing two screws at the end of the panel that keep it in place.
The top panel will take a dual 120mm radiator (up to 60mm thick). Top of the rear panel houses two holes for external watercooling.
With width of 230mm, Arc Midi is one of the widest mid tower cases around. That of course is a good thing since it will take pretty much any large CPU cooler. Maximum allowed CPU cooler height is 180mm.
The rear panel is characteristic for the white expansion slots. Fractal Design's cases are usually recognizable for black-white contrasts, which is the case with interior as well. Namely, the case uses white fans and fan brackets. Apart from seven horizontal expansion slots, Arc Midi has another vertical one, which can be used for the bundled fan controller.
The PSU goes in the bottom of the case and the dust filter can easily be removed.