I use Heathrow all the time for one reason or another.
I also have many friends who are either designers or Architects. I would tell you what they think of Heathrow particularly T1/2/4 but I'd probably get banned from this forum.
Let's be honest if you travel through any of the major world's airports such as Sydney, San Francisco etc, etc then Heathrow is like a third world airport. (although some of these are better too) Before I even start about the state of the decor - just look at the carpets, grey, worn and full or gum, and that's the first thing that greets passengers. Oppressive low ceilings, poor lighting, overcroweded. It's more like a series of pooly designed underpasses from a pooly designed 70's city than an airport.
London really does deserve a better airport and the truth is that if it doesn't get one pasengers and airlines will elsewhere.
And it can be done ! look at Gatwick, not perfect, but a great airport.