Obviously the security system is a total disaster. It's been discussed so much on here but the mind still boggles as to how they got it so wrong.
Also, BA/BAA missed a golden opportunity to hard-wire nice fast track channels into the design of the terminal. But no, they didn't bother, because they expected such efficiency there would be no queues, which now looks like misguided idiot optimism at best, and ludicrous arrogance at worst. Anyway, the result is now that fast-track feels a total afterthought bodge-job (and works like one too) because there wasn't really anywhere for it to go.
Same with the numerous lanes in the FCC. It's just so small and claustrophobic down there, and again, reliant on miles and miles of tape barriers. It's almost as if nobody thought about the requirements for that area and instead just decided to build a big empty hall then fill it with tape barriers when they'd worked it out later. Awful.
I suppose what I'm trying to say was, they had the chance to look at their requirements and then build something spacious, stress-free and pleasant, rather like the new terminal at SIN, but instead we've got another claustrophobic, over-crowded mess, in certain areas.
Shame because other bits, like the lounges, are exemplary.