As a former industrial controls engineer, what really bugged me was miserable engineering when it came to safety and ergonomics.
First, the Federation - and nearly every race they ever ran into - used flat-screen touchpanels for every control panel on the screen. Apparantly in the future nobody will ever use mechanical buttons or switches anymore; everyone switched over to fancy electronic interfaces as soon as they were technologically available. Thing is, flat-panel screens make for miserable controls. You can’t find a critical button or switch by touch, so you have to look down at the screen every time you want to use a control. There’s no tactile feedback of when you’ve actually pushed a button or not, so it has to beep instead. Ever tried touch-typing on a membrane keyboard?
We have the technology today to replace manual controls and keyboards with fancy computerized touch-screen displays. It’s a fine idea where you need the flexibility to completely reconfigure an interface screen, but using this kind of interface for something really critical like the buttons to fire phasers or eject the warp core is really stupid. Take a look at how the Space Shuttle’s cockpit is set up they’ve got the computerized “glass cockpit” screens for displaying important information, but all of the important buttons and switches are mechanical, usually with rails or guards around them.
Yeah, I know the real reason they did that on TNG was for budget - a backlit screen is much cheaper and easier than actually mounting hardware. But as someone who’se worked in process control engineering, it really bugged me.
The bridge of the Enterprise-D was a nightmare. Crew consules that required you to stand for your entire shift? Ramps and steps in the floor for no apparant cause. No seatbelts - a problem that every Star Trek incarnation has had. Consoles that exploded when some far-distant part of the ship was damaged - which is especially curious as the Enterprise’s communication network was supposed to work by fiber optics, which don’t conduct electrical power surges too well.
Federation engineering is not robust at all. Every control task on the ship - down to opening and closing the doors - is dependant on the central computer cores. While there are three of them, if all three go down the ship is completely helpless. This is a terribly fragile arrangement for a shpi that’s supposed to be capable of combat, even if not primarily a warchip. A far safer system would have somputation spread out as thousands of subprocessers around the ship, with a fault-tolerant network between them. We’ve got the technology to build this today, so the Federation really has no excuse. The power system is similarily a nightmare - from the fragile warp core with minimal failsafe ability, massively excess reactivity, antimatter injectors that can get stuck open and an emergency ejection system which never actually ejects quick enough, to the brilliant idea of distribution power throughout the ship in the form of plasma conduits.
Apparantly, sometime between now and the 24th century, we forget everything we know about ergonomics, distributed computing, workplace safety, high-power electrical transmission, and fail-safe engineering, as well as the secret of building such fantastic devices as seat belts, fuses, security cameras, and mechanical pushbuttons.