The internal CPU blower vent. If it was good enough for the glorified heater known as the Pentium 4, I'd like to see what that design would do for modern CPUs.
It feels like OEMs back then were more enterprise quality than. Even the enterprise desktop cases of today aren't built that good, but then again if you want an enterprise case, you might as well get a server rack.
I'm not talking about aesthetics, I'm talking about functionality. If there was a modern case like that G4, I bet the owner of said case would win contests to see who can upgrade ram the fastest. I'm not saying that case is useful for a race to upgrade components, I was using that as an example to demonstrate how swiftly one could upgrade ram.
I don't mind taking an hour or two to build a PC, but I hate fucking with it once it's already setup. I can't be bothered with looking for a screw driver to open my case or even if I had thumb screws, I don't want to worry about forgetting where I put them and that problem is worse with smaller screws and it would be nice to avoid that as much as possible. That G4 design was very efficient and I look forward to 2019 to see if other cases will have that motherboard door.
Though I like the stock colour, it makes it less of a theft target. Thieves be like "My GF has one and it's slow as fuck and I saw that shitty Dell at a Goodwill and it's not worth stealing because it's so big and not worth the trouble for $20. If it was a gaming PC or a Mac, it would be another story. Damn these guys need to join the 21st Century and get an iPad, that I can sell fast."
I wasn't taking about just aesthetics either... Cases have gotten better with space efficiency, air flow, cable management and durability. Advances material and sourcing of better steel/aluminum has led to cases that can actually last multiple rebuilds. Standardization of motherboard form factor and other components has led to much more compatibility and saved tons of money for everyone. The G4 itself has flaws, the latch for the door was rather chinsy, and after sitting around for a very long time, the plastic for the latch gets brittle and will fail along with the handles/feet for the case. I own one, it's an okay case. Along with the plastic, the steel in the case is rough and very soft, rather crappy steel, basically gutter quality (down to the galvanization on it).
Cases today are built from better steel, have tool less drive cages, and take into account things like cable routing, CPU cooler swapping and other nifty things right out of the box.
I won't say the G4 is a bad case... but they all have their flaws. If you plan on "fucking" with your build that much, perhaps a test bench is better for your purposes... and other cases have pulled off the same thing very well... like say... the Corsair Vengeance C70? Two very solid latches that need to be popped, have access to literally everything along with tool less drive cages and exceptional cable routing. Now not only can you swap out RAM really quickly, you can knock out some HDDs while you are at it.