It's actually amazing the Galactic Empire managed to control as much of the galaxy as they did. Logistically, they had the funds and the manpower of a giant imperial power but there were serious issues with the Imperial Defense Contractors.
Frankly, the Empire seemed to buy anything and everything.
Like the United States and Russia during the Cold War, the Galactic Empire obviously bought technology and weapon designs with little consideration for anything other than their ongoing effort to have the latest and greatest.
Some are just cumbersome and inefficient, like a moon-sized space station. Others were egregiously flawed from the start, reckless enough to be considered treasonous.
1. The Emperor's Royal Guards' Armor
With what armor do you equip the guys who guard the most powerful person in the universe? Bright red robes, of course. Then give them a giant, long, plastic helmet which restricts their neck movement and you've got a winner.
It's a good thing the Emperor moves like a senior citizen walking out of a Golden Corral, because his Royal Guardsmen only have a six inch slit in those helmets for what looks like a 60-degree range of vision. But that hardly matters anyway, because even if they had to defend the Emperor for any reason, they've been issued what looks like pikes to fight with in a world full of lightsabers and blaster rifles. Their unit patches should probably just say "cannon fodder."
2. TIE Fighters
When you need a fleet of superfast fighter spacecraft to defend your giant, lumbering Star Destroyers and planet-sized space stations, what better way to pump out a bunch of placeholders than the TIE Fighter, the galaxy's most elite floating targets?
With only two chin-mounted cannons, dual ion engines, these pilots are expected to tackle fleets of superior X-Wing and A-Wing fighters head to head, with the only strategy employed in their use being the Empire's ability to throw an overwhelming number of them at any given time. Also, there is not pilot ejection system.
On top of all that, they come fully equipped with a set of giant walls acting as blinders on either side of the craft, effectively restricting the pilot's vision of roughly half of the battlespace.
This is another example of the Empire favoring numbers over combat ability. The Empire's signature shock troops, the average Stormtrooper hasn't successfully killed anything since the Clone Wars ended.
The only exception was the Snowtroopers at the Battle of Hoth but lets be honest – the Rebel Alliance depended completely on ONE giant ion cannon to protect the entire planet from an invasion.
You might defend the stormtroopers by blaming their rifles but that's all the more reason to execute whomever procured the rifles and/or negotiated the clone trooper deal. The blasters would be a lot more effective if they didn't come permanently set to "miss."
Finally, the white PVC armor does nothing for them either. Why bother wearing bright white armor if it does nothing to protect you from the flaming death bolts the other side is shooting your way. Han Solo does just fine in combat and he's wearing a vest.
4. AT-ST Walkers
The All Terrain Scout Transport, the two-legged version of The Empire Strikes Back's famous four-legged snow invaders, are supposed to be an environment-adaptable version of the same. Except whomever convinced the Empire to deploy them on Endor didn't tell the Imperial Army about the height of the trees being taller than that of the walkers. It doesn't take a protocol droid to know how to bust into one of those from the treetops.
And if the AT-ST was the right tool for the job on Endor, it would have been able to navigate a series of rolling logs, the armor shouldn't have crushed like an empty beer can between two trees, and the Empire wouldn't have been beaten by an army of Care Bears.
5. Speeder Bikes for a Giant Forest World
While we're on the Battle of Endor, who put it in the Empire's mind that the ideal ground transport for scouts was a hyper-fast moving, one person bike in a world full of giant primeval trees? These bikes are begging to be wrecked left and right.
The Ewoks could have just set up random strings of rope all over the forest and taken out half these Imperial Scouts. Speeder Bikes on Endor are a safety brief waiting to happen. Even in Return of the Jedi, no one who drives a Speeder Bike ever lands one, they all just wreck or are punted off in some way.
6. Death Star Exhaust/Ventilation Systems
It's actually difficult to blame an engineer for putting a thermal exhaust port on a giant, roving space station. The thing's gotta have a tailpipe. Should it have led directly to the Death Star's reactor core? Why isn't there a few twists and turns leading up to the core?
They should have installed a few vents, maybe a more complex system would have worked better. Still, at only two meters, it's hard for any engineer to predict the effects of what is essentially magic on the trajectory of a proton torpedo.
Who we can blame are the engineers who designed the second Death Star's reactor core. Despite the lessons learned from the destruction of the first Death Star at the Battle of Yavin, the new team of engineers not only kept the big gaping hole design flaw, they made it so big it could fit the Millennium Falcon, two X-Wings, an A-Wing, and a few TIE fighters.
They didn't need magic torpedoes the second time, the Rebels just flew right up to the reactor core and blew it to smithereens.
Update: The Star Wars film "Rogue One" covered #6 on the list. The design flaw was a purposeful attempt to give the rebels a chance against the space station.
The author stands by his assertion that the second Death Star didn't need a hole leading directly to its core.