1. Lack of technology for differentiating safe and unsafe liquids. Its embarrassing when you haven't removed that extra bottle of water you packed on a hot day. (Come on EU!)
2. Lack of drinking fountains as you can't take safe liquids through security. (I could name certain airports.) Are they trying to blackmail people into buying bottle water at exhorbitant prices? That I really hate.
3. Claustrophobic holding areas at gates (the US may be maligned but there airports are generally have good open plan terminals
4 - 10 queues and waiting - you can probably think of at lease seven places where you have to queue on an international journey (security, boarding, immigration, baggage reclaim etc.)
That said give me an unobstructed view of the airfield from the terminal and I love airports. Indeed I'll deliberately check in early at some (not all) airports to spend extra time airside.