Probably stormtroopers not being able to shoot. I mean I don't want the rebels to die, but the imperial TROOPS should be able to SHOOT! even in a HALLWAY!
The fact that Ewoks existed. Also the fact that they made a second Death Star, with the same exact flaw...
Actually I believe Death Star Mk II didn't have that flaw, but instead they were flying down an area under construction (have to get materials into the belly of the ship, so you need "crawlspaces"
Hardly a flaw. The fact that they were able to make exhaust ports so tiny on such a massive ship is **** near a miracle
The flaw was having them lead straight towards the reactor (on top of the flaw of putting so much effort into one basket)